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The connector is the same (and it's shitty) but the signaling is very different

The connector is not shitty, it's a fine piece of work in terms of capability, ergonomics, form factor, mechanical stability and basically all the things that matter about a connector. Thunderbolt 3 conforms to USB Type-C physically, electrically and protocol-wise, using Type-C's "alternate mode" functionality to provide PCI-E and DisplayPort functionality. So I take issue with your "very different" characterization, it indicates that you have not bothered to read the Wikipedia page or "Thunderbolt Technology Community" page, or any other accurate information. (BTW, you'd be an idiot to trust my post too, just go right ahead and check it.)

USB-C and its Thunderbolt 3 superset are high minded, ambitious projects, apparently well executed, but with obvious potential for compatibility nightmares. We are right now on the verge of finding out just how bad that is going to be. Let's hope for the best.

What you can connect to what depends very much on the controller hardware on each end and the software driving that controller hardware. For example, to connect a monitor you need hardware such as DisplayPort, which is (apparently) always supported by Thunderbolt 3 controllers, but does not necessarily require Thunderbolt 3 because it is one of the "Alternate Mode partner specifications" defined for USB Type-C. HDMI is another alternate mode partner specification defined for USB-C. Apparently, Thunderbolt always provides HDMI 2.0, but this can also be provided without Thunderbolt. Confused yet? You should be. If not, then you just don't understand.

Aren't most USB-C docks with video output actually Thunderbolt docks in the first place and don't need any special software?

I don't have a USB-C-equipped Mac, so I only know so much about this; but...

I believe the answer is "No". There is a complicated relationship between USB-C and Thunderbolt 3, and I believe that you are correct in stating that a TRUE TB3 Dock would NOT require a Driver. But the USB-C Docks that are "Thunderbolt compatible" aren't REALLY TB3 at ALL, and actually use a different protocol out of the USB-C port, which I believe requires some interaction from the Peripheral-side of things to get the USB-C/TB3 controller in the computer to spit out the video datastream.

Sorry, that's more than all I really know about how all this works.

This might help:

https://thunderbolttechnology....

And this might confuse you further... ;-)

https://www.cnet.com/how-to/us...

Perhaps a HDMI-C plug will be on the card in 20 years or so?

No need, video over USB-C is already a thing.

Look again at the PDF you linked to, HDMI is listed on the second page, left hand column, first paragraph.

You'll also note that the document I linked to, as well as the one you linked to, are both from 2016, after Thunderbolt 3 co-opted the port. If you look at what was supported prior to that, the USB-C spec itself, you have USB, DP, and power distribution. HDMI Licensing did release a standard for HDMI over USB-C in 2016, as well, which is separate from the Thunderbolt 3 standard which already included HDMI over DisplayPort. It is also worth noting that the Thunderbolt 3 standard includes 8 DisplayPort lanes while the USB-C standard includes only 4.

The way HDMI works, using all four data lanes in the spec, makes me wonder if a USB-C port could support both Thunderbolt and HDMI at the same time like Thunderbolt and DisplayPort can share data lines.

Since USB-C itself provides only 4 DisplayPort lanes, HDMI uses them all, and the port cannot be in both USB and Thunderbolt mode simultaneously, I would posit that this is not possible. It may be possible to slip some USB data in with the HDMI stream if the resolution or framerate is reduced sufficiently; I honestly don't know enough about HDMI to know if it frees up some of those lanes when it doesn't need the bandwidth. That said, as Thunderbolt 3 provides 8 DisplayPort lanes, a USB-C port operating in Thunderbolt mode can provide display and data transfer simultaneously, even at 4K@60Hz. If you have Thunderbolt available, that's what you'd want to use.

It was my understanding that Apple supported HDMI on USB-C and the adapters they offer for HDMI are passive, but I may be mistaken.

There was no HDMI over USB-C spec until 2016 and the current MacBook models still have the same chipset as the 2015 models. Additionally, the USB-C port, when not operating in Thunderbolt 3 mode (which these models lack) can't pass video and USB at the same time, thus why Apple sells a USB-C to DisplayPort cable (which, in theory, should work with a passive DP->HDMI adapter, as well) and USB-C adapters which include a second USB-C port, a USB-A port, and either HDMI or VGA. If the adapters were simple passive circuits, the USB-C and USB-A ports on them would be nonfunctional while video was being passed.

Intel does license Thunderbolt to others, AMD included.

Since when? The article you linked to, published less than 6 months ago, states that "Intel hasn't made the specification available to other companies" and "Intel has unveiled plans to not only build the technology into its processors, but to open the spec through a non-exclusive, royalty-free license." I see no indication that either of those things has happened yet. That might be why AMD does not take advantage of it. In fact, this article, published by Intel the very same day as the one you linked to, states "ntel is announcing that it plans to drive large-scale mainstream adoption of Thunderbolt by integrating Thunderbolt 3 into future Intel CPUs and by releasing the Thunderbolt protocol specification to the industry next year." That pretty much confirms why AMD hasn't taken them up on the offer yet; and time will tell whether Intel will make good on their word.

I hope they will, but I've had business dealings with Intel before and, let's just say their word is only as good as the legally binding contract it's written on, and that article is not legally binding.

I'm not saying it's not a problem, only that it's not something I'm going to be terribly concerned about now that I know some more about the issues.

I'm not terribly concern

When it comes to devices falling back to USB 3 if the cable or host system don't support the Thunderbolt protocol does not make much sense to me. What devices would you want/need such fallback? A hard drive might make sense I guess.

Hard drives, network adapters, audio interfaces, printers (do Thunderbolt printers exist?? I bet one does somewhere), scanners, there are a number of cases where it makes sense and those are just the ones I can come up with off the top of my head.

With a network adapter falling back to a lower speed is not always desirable. Sure, a 10Gbps Ethernet falling back to 5Gbps might not be a deal killer. If you are investing in a 40Gbps network adapter then having it not fallback to 10 or 5 Gbps USB speeds isn't going to be deal killer. Such people might even prefer it to not work since it exposes a very real connection problem rather than hide it with a fallback. Audio devices, printers, and many other devices are such low bandwidth that there is no need to supporting Thunderbolt, USB 3 or even USB 2 speeds is enough. I could be convinced to give in on the network adapter, since falling back to a lower speed on a network might be desirable in some cases, as opposed to not working at all, much like the hard drive, but the other examples you gave are not likely to see an advantage from the higher data rates of Thunderbolt over USB. Falling back to USB 3 is nonsensical since its nonsensical to have Thunderbolt in the first place.

When did we start to see this regression into USB-C confusion? Where you needed device or protocol specific USB-C cables?

When Thunderbolt 3 co-opted the USB-C port, of course. Since then, I haven't bought a single USB-C device that didn't include a cable and a warning to use only the included cable, as other cables may not work.

I'm not so sure. I can understand why someone selling a Thunderbolt device might say to use the cable that came with it. This is not much different than someone selling a USB 3 device and saying to use the cable that came with it. I've seen this going back to old serial devices, parallel port devices, and on and on when the quality of the cable and/or differing pin outs on cables with the same connector might be a problem. The old DB-25 might be serial, parallel, SCSI, or something completely different.

Where I'm frustrated is seeing cables that will support Thunderbolt 3 but not support USB 3 at it's full 10Gbps, or even 5Gbps. I've read that Thunderbolt 3 is a superset of USB 3, says so on Intel's Thunderbolt FAQ.
https://thunderbolttechnology....

I thought that to mean that since Thunderbolt 3 is a superset of USB 3 then a cable that meets the Thunderbolt 3 specification would support USB 3 at "super speed" data rates. I was disappointed to see a Thunderbolt 3 cable, on Intel's website, that did not support USB 3, maybe not even USB 2. Careful reading of the claims tells me that the *PORT* specification is a superset of USB 3, but that is not claimed of the cables. Intel created this confusion by not enforcing this idea of Thunderbolt 3 as a superset of USB 3 on the specifications for the cables. Might this enforcement mean more expensive cables? I assume so. That's probably why Intel allows this confusion to exist, the cables already cost quite a bit and by allowing Thunderbolt only cables they can better compete on cost. This comes at the price of confusing even their technically informed customers.

So many manufacturers have non-compliant cables and devices that finding ones that work as they should may be nearly impossible.

This is where the USB and Thunderbolt groups could have worked together a little better. They could have come up with some sort of labeling or color-coding requirement for ports and cables, such that you could glance at it and know w

Thunderbolt 3 is fierce and could do it. The issue is always market, even with standardization.
Meanwhile we have morons like Palmer Luckey attacking Apple; basically the kingmaker in pushing to market modular, externalized resources like Thunderbolt 3 / USB-C.

Apple has pissed off all the other CE manufacturers. There will be nothing to plug the other end into. Without general support great features are worthless. Apple is repeating Sony's mistake with betamax. They won't share, thus it will fail. Great technology without support is worthless.

Don't own any professional equipment or work within the NAB world? Do some more research. More and more manufacturers are jumping on-board. https://thunderbolttechnology.net/products