[ward]

NB: I used to help with STK development around 2011-2013, so have a likely biased view in this particular discussion.

Actually, SuperTuxKart definitely moved some things away from Sourceforge already. You can find the Github account at https://github.com/supertuxkart. (Finished) assets and their "development" files (blender files, lossless audio, ...) are still on Sourceforge. I have not been actively involved with the project in a few years now, but as far as I am aware this is due to the simply enormous size that assets take up in a game. The finalised assets download is 650MB, the originals is 1.5GB (see http://supertuxkart.sourceforge.net/Source_control). Due to the nature of svn this is only the current HEAD, you can imagine how big of a git repository this would end up becoming, where you by default download the entire repository. (EDIT: Github allows repositories of up to 1GB in size, see https://help.github.com/articles/what-is-my-disk-quota/)

Furthermore, up until recently I believe Github severely limited the size of binaries you could upload. You understand this puts them at an impossibility.

Also, Sourceforge provides mailing lists, Github does not.

The wiki could be moved from Sourceforge to Github, but I do not know if that is a project they currently feel like undertaking. The current setup uses mediawiki and is easy enough for non-developers to update as well as having the same style as the landing page. If you switch to Github wiki, then the style breaks completely with the rest of the STK site. If you switch to a project page by means of the github pages, then you make things (I believe) significantly more difficult to update for the less technically oriented volunteers.