I'm sure they can get a MIDI adapter working because it already works if you use the GH:WT drumkit.
I posted about it not working but it turned out to be a bad MIDI cable. So right now I'm connecting the GH:WT drums to the Legacy Game Controller thingy and plugging my e-drums into the MIDI port on the GH drums and it works fine. So it's totally possible to do a wireless MIDI adapter.
It's due to Microsoft not allowing wired controller data at all at the moment.
The GH:WT works because it's wireless and is a tightly controlled (literal) air gap between the One and the drumkit. I'm also curious if your e-kit is actually able to do full pro (it didn't let you do it in RB3) or if the GHWT drumkit is just intercepting MIDI commands and converting them into GHdrum note commands. The MIDIpro actually passes full midi data to the game, which is why it was wired.