the ISO button on the right/top side of the camera will certainly be accessible by housing manufacturers. However, with the right hand already so busy during uw shooting (focus initiating, shutter release, change of aperture and shutter speed, stop flash, start video etc.) and now in addition to change the ISO sensitivity, this seems to me a step back in ergonomics. Hope there is still another button to reassign the change in ISO to be used with the left hand (although I understand that the Mode button cannot be used for that). let's see!
But for me there is anyways no real reason to upgrade, neither for camera nor the housing (and thus even saves a ton of money...)