I wonder how many users will come to depend on it before they shut it down.
My impression is that the monolithic repository only works because Google's built a bunch of custom tooling to support it. It doesn't mean any company can just roll all of their code into a single Git repository and call it a day.
The key here is CITC. All the source code lives "in the cloud" and pulls to your machine as it's needed (using a FUSE file system).
It was a full-blown social network for a while.