> USB-C oscilloscopes work because the peripheral contains all the hardware, so it doesn't particularly matter that the device->host latency is high.

Yeah, that's basically the way accessories have gone. Powerful mcu's and soc's have gotten cheap enough to make it viable. Makes me a little sad though, I liked having low latency "GPIO's" straight to software running on my PC (but I'm thinking as far back as the parallel port... love how simple that was).