Visual Studio Online supports Git. So, no, it is not "TFS in the cloud." TFS and Visual Studio Online are very loosely coupled.
> Are you confusing TFS with Team Foundation Version Control (TFVC)?
I'm not confusing anything, I just picked one of Microsoft's many acronyms they use for it. Even Microsoft's own consultants call it "TFS" when talking about Visual Studio Team Services in Visual Studio Online. So if Microsoft's own consultants are "wrong" then I am in good company.
> I don't think TFVC is going anywhere anytime soon.
I do.
It doesn't work very well: it sends way WAY too many files up and down constantly, it has no concept of a pull request, offline mode sucks, branching/merging is expensive as all heck (inc. disk space, bandwidth, time, any metric), and even Microsoft's internal teams are utilising Git and Github.
I've used both on VS Online, no comparison, and Microsoft's own staff seem to agree. It is only a matter of "when" not "if" TFS will die and Git will take its place (although I suspect Perforce will survive on the Windows team within Microsoft).
There's a reason Git has taken over the world.