A virtual file system to show releases in a consistent way using conventional tools rather than command line tinkering and web pages. You could even edit/compile/test/commit directly into Git.
A caching subsystem. E.g. there is so-called Git Virtual File system from Microsoft that does that.
A project management system (rather than messy file management).
Thanks for the link, but that does not look like project management where you can walk releases of a project and get a consistent view of releases of all other projects linked to this one.
I would use it as a backend. Like any other file controlling system (Perforce, MKT, Subversion) Git is just a database you can drop into and take from versioned files.
It should be fast, allow storing artefacts (object and executables), support locking (e.g. to prevent or at least keep under control merging/branching madness). The rest can be implemented on top: views, releases, release related source adjustments (like placing version info into files), automatic tests. automatic release install/packaging, automatic release update builds etc.