Yeah, we're talking multiple multi-billion dollar industries. That if the main players won't service them will be serviced by niche players who do. You won't find a USB anything version of an SDI capture card worth (they exist, they're just universally not good) a damn or used in a professional broadcast environment because USB, by de facto, doesn't lock and is temperamental. You will struggle to find a USB multi HDMI capture card. Forget about putting multiple USB capture devices on the single shared USB connection integrated into your motherboard. A motherboard with 12+ ports usually has three distinct USB controllers, only one of which is worth a damn. There are PCIe machine vision capture cards that have onboard GPUs and dedicated co-processors so that the machine vision algorithms can run directly on the PCIe card and never involve the CPU nor have to move the captured video across the bus to main (usually far slower) DRAM. USB has incredibly high latency, and more importantly, non-deterministic latency, which is why USB MIDI on the desktop is fine for casual use, and lousy in an event setting or a professional recording studio.
USB has incredibly high latency, and more importantly, non-deterministic latency
Seeing that RME's USB 2 interfaces manage to stream like 50 or more 24bit audio channels at 48kHz with buffer size small enough to get latencies in the mSec ranges, I always wonder: are other manufacturers just doing it wrong? I know that doesn't completely cover the non-determinism argument, but 'incredibly high' seems to be covered pretty well.
The RME-Audio devices do indeed have low latency, at the limits of the USB 2.0 spec, 125 microseconds I believe. They crank up that USB poll rate. And are also using the Arasan chipset IIRC, the same to be found in some of the other prosumer and pro line-up of equipment, e.g. the Solid State Logic h/w. I am hazy on the details, it has been a few years since I was inside any of those devices, people from RME and SSL please feel free to correct me as to your chipsets. Some are using dedicated FPGAs to handle the data capture and processing before handing off to USB. RME's devices are definitely doing a bunch of on-board processing before giving it to the USB bus, and making sure the packets going out are as small as can be. Most non-integrated USB controllers are using VIA or Renesas. USB 2.0 has lower latency but less consistency (shared bus) vs USB 3.0 which has higher latency but is more consistent (point-to-point protocol). Obviously you don't want to go sharing your USB 2.0 port on your PC with an RME and a bunch of USB 3.0 devices, e.g. an external drive, because then you just end up with the worst of both specs, terrible latency and terrible consistency.
If you went into Best Buy and asked 100 people this question do you think they are wanting that?
Your use case scenario is very much available from every major computer systems manufacturer, it's just list available under the "Professional" "Workstation" category, not the "consumer/prosumer/a computer is a computer".
If you're saying you don't want to spend the money I get that, but between assuming your use case is the majority.
SAS is not consumer. Multi HDMI capture is not consumer. But all these solutions are available in a different market, which are also much high quality.
EDIT: you also mention U2 drives... If you're expecting to use that in a consumer PC you might want to check your expectations. Maybe 15 years from now they will be the standard but they're firmly in the enterprise market.
You kinda wasted your time there, since I work in one of those very industries and know most (if not all) of this. I just asked whether you really thought it works be worth the major players' time. The use of the word 'niche' was telling.
