You don't really need it anymore - CitC let you do views (mapping just part of the monorepo into your filesystem via FUSE) since about 2013, and then that functionality just got built into Piper. When I returned in 2020 you'd have a file at the top of your source tree that included all the relevant file mappings as well as any Blaze flags needed to build the project, and you could just point your IDE at that and it'd map in just what you need.

The history of Google's relationship to version control is even more interesting than editors - it went from CVS in 1998 to Perforce (P4) in 2000, then gcheckout and g4 in ~2006, then OverlayFS was invented in 2008, git5 came out in 2009, CitC obsoleted OverlayFS in ~2012, Piper built this all into the VCS in ~2013-2014, while I was gone from 2014-2020 apparently we got hg and jujutsu frameworks, and then when I got back in 2020 you'd just check out a .blazeproject from your IDE and everything would magically work. Many of these started as 20% projects (I used to have lunch with the guy who invented OverlayFS; interesting character and one of the best programmers I knew) and then got folded into the "official" way of doing things once grassroot adoption showed the execs that this was how people really wanted to work.