They do mention that it supports virtual file systems through Sapling, which now encompasses their long known EdenFS. I'd like to know more but right off the bat Sapling says it is:
> Sapling SCM is a cross-platform, highly scalable, Git-compatible source control system.
Git compatible eh? Thats a lot less foreboding. (It is however a total abstraction over git with it's own distinct cli tools.)
I hope there are some good up to date resources on Sapling/EdenFS. I have heard some really interesting things about code kind of auto getting shipped up to the mothership & built/linted proactively, it just at commit points, which always sounded neat, and there seem to be some neat transparent thin checkout capabilities here.