I think it's too early to say. The devs have assured me that MIR itself will land within the year, but beyond that point I think that non-lexical borrows might be out-prioritized (though just barely so) by incremental recompilation.

I'm not sure I can say for sure when they'll be ready, as MIR isn't 100% done, and they're built on top, so it's tough. There's also the difference between "lands in nightly" and "lands in stable", which could be some time for a feature so large.