Does anyone know of any tools for extending the functionality of Sharepoint's existing version control system for Office documents? It'd be great to be able to do branching/merging, or to store versions as "deltas" off the previous to cut down on storage used.
Any suggestions at all would be helpful. Thanks in advance!
SharePoint document versioning is internal to the server architecture, and cannot be extended.
It sounds like you want to use SharePoint as a Subversion client. There's no practical way of adding branching or versioning off change deltas without a full rewrite of the out of the box versioning.
If you have a healthy amount of time to devote, i'd swap out the SP versioning system and roll one with a Subversion backend