Oh and I just realized, this means if you have both versions of Halo 3 or 4 and you want to do customs or matchmaking on one them, you have to pick a version-- I thought about that hurting the Halo 3 and 4 matchmaking populations on the 360, but it won't help the populations on the other console, and it makes customs more complicated and difficult by lowering the populations for each one and introducing that choice because people will have a preference or just not have one or the other.
*sigh*
This will probably be good overall. I'm confident in predicting a rise in custom games, and a significant one, more than enough to be significant, even. It has a cost, though, and however feasible or plausible it might or might not be, I wish the cost was less.