well, no, the web audio API & stuff is explicitly being sold as something that will be equal in capability to other solutions, so definitely things used for pro audio.
It seems like a relatively contained problem to take multiple streams of PCM audio into a computer, locked to word clock. Then the hard, fiddly aspects of analog design can be left to high-quality outboard converters which speak MADI or whatever.
I say "contained" because I don't want to minimize the difficulty of getting such a design right, but it seems like you only have to get it right once.
Then we don't need a USB driver for each converter! We only need one USB driver, for the digital i/o interface. And we can polish the driver for that one interface until it's actually reliable, instead of relying on the sketchy one-off driver for this year's soon-to-be-obsolete USB audio interface.
ETA: Many such converters (most of them high-end) listed here: https://www.sweetwater.com/c796--AD_DA_Converters
If I'm not mistaken the underlying transport protocol is the same for all of those - you can get a coaxial to XLR to get S/PDIF into an AES port or a coaxial to TOSLink converter to get S/PDIF data into an ADAT port.
You can look into the Madiface XT maybe ? https://www.rme-audio.de/hdspe-madi-fx.html or the other RME products which have enough digital I/O to cover a lot of needs
But the point is that I want open source drivers, and open source hardware! I don't want to depend on the health and the priorities of a commercial entity. I want to be able to inspect the driver software and contribute towards perfecting it!
Compared to, say, GPUs, the needs of multichannel digital audio i/o are modest and not changing very much over time.
Some quick usage of Wikipedia suggest that you are, sadly, mistaken. ADAT lightpipe seems to use a completely different protocol (more capable?), and while S/PDIF and AES/EBU use quite similar protocols, they differ in impedance and max and min voltages, so I'm guessing that directly electrically connecting the two controllers is a bad idea for both the controller and the data.
(Licensing could be a concern though if ADAT lightpipe is proprietary — I'm not clear on that. But then we could just use other open protocols instead.)
I mean, I have currently 5 soundcards on my desktop computer, 1 pro over PCIe, 2 pro over USB, 1 standard HD Audio and 1 output in my screen's HDMI, and I can assure you that even on windows it's definitely not a smooth ride between WASAPI, ASIO, MME, WDMKS... things crash or get stuck routinely, and I sometimes get random loud buzzes or no sound until I reboot. With my band we had tons of issues with a M-Audio card on windows fixating itself on the wrong sampling rate as soon as a desktop music playing was launched (this includes web browsers), entirely preventing playback on Ableton Live for instance.
It's barely better on macOS, e.g. look at that shit: https://github.com/OSSIA/score/issues/778. macOS also sacrifices some low-latency when comparing the same hardware on it versus Linux (with raw ALSA or JACK) and Windows with ASIO.