I was looking at that, wondering what's missing.
You'd definitely lose:
Af/WB - changing autofocus / whitebalance modes (might not be a big deal if shooting raw anyway)
Drive - changing from single shot to multi-shot (no big deal)
Metering / EV compensation - (shouldn't be a big deal underwater)
Trash - (not good, but not the end of the world)
On / Off - this would be bad, you'd have to turn the camera on before it's in the housing, then make sure auto poweroff isn't set.
Might lose:
Menu (ouch, can't change iso easily any more, unless you tie it to the set button)
Info (no prob)
Jump (no prob)
Magnify (no prob)
Play (bad, but you could set the review time to 8 secs and just deal with it)
You could probably deal with it, but I wouldn't want this to be a permanent solution. Probably could deal long enough for the housing mfgrs and bank account to catch up...