What's a normal range for Bluetooth headphones? Because I was pretty amazed to still have audio playing on my AirPods being ~75m away from my phone. To be fair, there was nothing but a single pane of glass between the two, but still, that's quite the distance.

The main issue is likely to be latency and lack of existing low latency protocols - it's doable, I use jack over my network to watch video and voip apps like Mumble get pretty damn good with compressed audio, but most of the music oriented type stuff is high latency SHOUTcast or other http streaming type solutions, which tend to involve large buffers and stuff. There's just nothing existing which would feel correct for wifi headphones to my knowledge.

Battery life is probably an issue too, but with low power wifi SoCs like the espressif stuff, you can probably get away with similar to Bluetooth using the tech that's around now and doing as much possible in hardware and with interrupts as possible.

Custom radio on ISM bands, works flawlessly

Would imagine wifi sucks too much power