I wouldn't expect a centralized revenue sharing scheme to happen. That becomes a singular point of failure, is ripe for abuse, and is kind of anathema to the whole space.
Small servers aren't that expensive to run. A space hosting a few dozen or a couple hundred users can probably be supported by any admins with the means to set it up in the first place. And if they're not, for some reason, then hopefully the admins are transparent, and the people that are there are actually some kind of community that can lend direct support.
Most of the groups are hosted on larger sites, though. That's where the content is. It would be nice to see them spread out a little more, but we need the ability to migrate groups to new instances before that can happen in earnest. In the mean time, splitting donations across multiple instances that host our favourite groups is probably the best thing we can all do.