CVS and SVN are probably a bit better at scaling than (stock) Git. Perforce and TFVC _are certainly_ better at scaling than (again, stock, out-of-the-box) Git. That was their entire goal: handle very large source trees (Windows-sized source trees) effectively. That's why they have checkout/edit/checkin semantics, which is also one of the reasons that everybody hates using them.

GVFS intends to add the ability to scale to Git, through patches to Git itself and a custom driver. I don't think this is a hack - by no means is it the first version control system to introduce a filesystem level component. Git with GVFS works wonderfully while offline for any file that you already have fetched from the server.

If this sounds like a limitation, then remember that these systems like Perforce and TFVC _also_ have limitations when you're offline: you can continue to edit any file that you've checked out but you can't check out new files.

You can of course _force_ the issue with a checkout/edit/checkin but then you'll need to run some command to reconcile your changes once you return online. This seems increasingly less important as internet becomes ever more prevalent. I had wifi on my most recent trans-Atlantic flight.

I'm not sure what determines when something is "a hack" or not, but I'd certainly rather use Git with GVFS than a heavyweight centralized version control system if I could. Your mileage, as always, may vary.