I think asking for what features to be included at this very early stage is probably not that important. IMO, I would concentrate on getting a good base system developed.
Allot of existing forum software failed to do this and this is why allot of forum software is poorly designed and hard to work with.
I would concentrate on getting the basic down. You'll need a flexible ACL system, good user tracking and above all a good system for implementing plugins.
SMF for one has an absolute nightmare of a system for integrating plugins. IMO plugins should not put code into the core of the application. Take Wordpress for example. While not really implemented as well as it could be, they do have a good plugins system based on events that allow plugins to extend the functionality of Wordpress without ever modifying the Wordpress code itself.
Most of the features mentioned above I wouldn't even really consider building into the application itself. They should likely be built as plugins, even if they ship with the software by default.
As for a SourceForge page. SourceForge is so last decade man, all the cool kids are hosting on GitHub these days.