For a wireless update you need to be able to store the new firmware in a temp area, verify it and then activate it. Old devices don't have enough memory but that's changing. Also, most new firmware needs new hardware features so this capability may not be that useful in practice.

It's more than liability, reducing physical access requirements opens up a much larger attack surface.

I know if someone's opened up my skull. I assume everyone has some sort of multi-band wireless transceiver in their pocket, because that's a cell phone.