Honestly any of those advanced features that might
not be available, I doubt any would be really necessary in the first place. It's just a plugin repository. Should be fine as long as you can pull, push, and merge.
As far as GitHub vs BitBucket, I think one of GitHub's great features that would make this a lot easier to manage is it's organization's
feature. Just as is used by TextMate
. As many people as necessary can be added to the organization and along with it comes fine grained access controls for each member and much easier management of the repos. Instead of having one user having to pull everything in, everything can be organized under the organization and multiple people can help out. Also all the repos will be under the ST organization so if someone runs out of time to contribute it's not tied to their account and it won't be some crazy nightmare trying to get everything under someone else's account. As far as I know BitBucket has nothing like this and personally I view this feature as invaluable in such a community project.
A small aside, Git is officially supported on Windows via msysgit and cygwin.