[SeanLuke]

Connecting a controller keyboard to a laptop isn't an issue because it shares power and ground with the laptop. But synths on separate power are another issue entirely. For example, the Waldorf Blofeld has a USB MIDI connection; I attach mine to my Macbook Pro and its audio presents a ground hum and an electric buzz whose pattern matches the Macbook's processor utilization. Attach via 5-pin DIN MIDI and the problem is gone.

USB wasn't designed for this use case, and it is a very, very common problem.

[TheRealPomax]

Except sometimes it is: I have an audio workstation with two "yellow" USB ports (as opposed to standard USB2's black and USB3's blue) that are dedicated audio USB ports with additional circuitry specifically for connections to audio devices. My Komplete Audio 6 kept buzzing and letting me hear my cpu activity in my old system (is it both amazing and the most annoying thing ever to hear your mouse move as HF signals), and has had perfect audio since switching to those for-audio USB ports on the new motherboard. As far as I know only Gigabyte makes these (my specific board is a z170x gaming 5) but they exist, and they're great.

Certainly, UBS in general can't be used for this purpose, but if there's true industry buy-in for MIDI over USB then it's not hard to imagine more and more USB hardware will get made that can compensate for that problem. For instance, I wouldn't imagine laptops to get isolated USB, but a shiny new post-MIDI-2 audio interface sure would.