I had a funny conversation with Madhu Sudan yesterday, with him relaying an idea he said he heard from Umesh Vazirani (and perhaps the trail goes on further from there) -- roughly that FOCS should double in size and STOC should halve in size. Or, I guess vice versa -- the point is that right now the two are pretty symmetric, and it's not clear that's the best setup.
The idea (or my interpretation of it) is that in theory we could use a more selective "top" conference -- one that people felt they should really try to go to, even if they didn't have a paper in it, because it would have the major results from the year. Hence we halve one of the conferences and make it more selective (and, naturally, make it single-session, maybe have some special tutorials or other activities). At the same time, we don't want to lessen the number of papers that currently are taken in FOCS/STOC -- indeed, since the community (or at least the number of papers being written) has expanded, we should probably accept more. (So maybe people wouldn't feel the need to start yet more conferences, like ICS.) So we double the other. Again, this would be a conference that, ideally, more people would attend, because more people would have papers in it. Indeed, this could help get papers out of the system faster (instead of papers being resubmitted quite so frequently). By introducing asymmetry, perhaps we could make both conferences more appealing and better attended.
I pointed out that one community I know of already does this -- this is very similar to SIGCOMM and INFOCOM in networking. I think that model works, though there are certainly tensions and problems with it -- as you can see in the comments on my recent post on Ranking Networking Conferences. (Bigger conferences are more variable in quality, primarily; also, they require large-scale parallel sessions.) Again, we'd have asymmetry -- the larger conference might become perceived as "weaker", but it would play the important role of bringing the community together and being an outlet for more papers.
Interesting as though the idea is, I have trouble imagining the theory community moving in that direction. Big changes are always hard to get moving, and it's not clear how many people really think the current system is broken -- though the ICS movement clearly seemed to think something was wrong. I'd be willing to try it, myself, but of course I also like the "two-tiered" (or maybe 1.5-tiered) SIGCOMM/INFOCOM system.