The way I'm reading the comments here, it seems that the solution that would work for the majority of people (except those opposed to thread proliferation) would be to have single-show threads for every show we want to discuss. And I don't think that's really feasible.
My only idea for keeping TV discussion in Natter is to use Natter as a watch-n-post, night-of-airing venue, with whitefont -- the way it always was for everything but Buffy and Angel, once upon a time. At least for those people who don't want to be spoiled for other shows. I agree, though, that having discussion of the same show in different places is logistically confusing.
If anything, I think one of the things this experiment clarified is the way people use the board. I have a hell of a hard time keeping up in Natter, and while skimming through white font about a show I don't watch should make that easier, I usually end up skipping to the end of the thread anyway, if I'm really pressed for time, so I never discussed TV much in there anyway.
I don't like the fact that some of us feel board culture has changed, although I agree with SA that the ship might have sailed in any case. None of which is really useful, I know, but I wanted to say it anyway. I'm a big compartmentalizer, so the threads worked well for me, even skipping discussion of shows I had missed. But I'm also, as noted above, an egregious skipper and skimmer, and miles of white font kills me after a while.