Mark Michaelis, a SourceSafe MVP, posts to his blog the following:
Unfortunately I can’t comment on the future of Visual Source Safe except to say that significant work is being done in this area. If this MSDN chat is any indication, the demand is huge as the entire chat is essentially consumed with, “will the next version support…” type questions.
It’s great to hear that there’s some progress being made. As the author of the only currently-available book, Essential SourceSafe, I’ve contacted aa number of Program Managers at Microsoft trying to get involved in new versions, and finding out if a revision to the book might make sense. I was surprised at finding SourceSafe 6.0d in my latest MSDN shipment without a word it was coming.