Nice, excited to see that. This is basically deeper pipelining, IIUC. Nick (the author of the blog) implemented the current version of this "emit metadata sooner," optimization and already experimented with pushing it even sooner a while back.

We have discussed this briefly on last All Hands, the problem will probably be dealing with compiler errors, when they happen in builds that already emitted metadata. I believe this was the reason why it wasn't merged in the first place.