The single, killer feature I'm looking for in a document management system (besides collaborative environment that we're used to from gdocs) is a way to stamp versions and have those be reviewed independently, with git like diffs across them. Think gerrit for docs.
The diffing isn't there, or at least not to the degree that code review tools offer.
I'm not sure the feature has evolved in years either. Definitely feels like one of those things a Google engineer threw into production one day, and it's never been considered again.