@Keavon closing because I'm not rebasing this yet again, I only just finished rebasing it the first time. Thanks.

I'm always happy to rebase things, just send me a message. I'll do this one now.

Rebase is done. That only affected about 5 small conflicts, so I'm glad to see my name updates aren't causing too many nasty conflicts.

@Keavon if you rebase, please make sure the code actually compiles…

This will instead be solved by the more generalized approach of #2988. But this was a really cool prototype, thanks for exploring this approach, it was valuable to learn from.