sourceforge already does integration with git, svn, and mercurial. The problem is that they basically are just hosting a repo then, but can't do advanced options easily because they support all 3.
Honestly, probably the top things imho:
1. allow feature requests that the dev can put a price on, and people can donate toward specific features.
2. Better source code integration like github has, even if only for git.
Some fucking markdown on slashdot would be great too. Typing html tags into comments is so fucking dirty.