oh, and WRT MrScout, I don't really know what to suggest, other than putting his "very important" stuff in a box in every room, in the hope that he will sort it, but by the sounds of it, I'm not sure you will have the space for a big enough box!
Does he understand how much his clutter is annoying you? I don't really know what kind of poorly you might be when your treatment starts, but could you explain that it is (by the sounds of it) bringing you down? and that if (even some of it) was put away (perhaps in the living room so you could easily have guests) round it would make your life MUCH easier & you MUCH happier?
I guess his hording is partly habit? (like your decluttering has become! 
) and he can't be expected to totally change overnight, but perhaps he could try to keep one room clear? (you may have to forfit another one though!)
When I started decluttering, I found it very difficult to get rid of some things, for example books (just paperbacks I was never going to read again) so I looked through them & chose just a few to give away. Then a few weeks later, I did the same thing. and again, and again. Would a teeny-tiny baby steps approach like that work with him? Perhaps the fact that he doesn't have to sort it ALL out at once, just get rid of a little bit of it, would make it easier?