A grab-bag of context:
- I maintain one of the crates implementing this.
- I had put together both a PR implementing this and an RFC exploring the idea
- The latest plan I'd heard around this was to fold this into the wider safe transmute effort. Basically to keep introducing alternative means of doing most of the things
asis used for (which is making progress), and when they're down to a small number, reframeasto be sugar for something that isn't compiler magic (e.g. as sugar forInto, or similar). See As Casting Reform: 2024 - HackMD for more discussion here.
Allowing From and TryFrom to be derivable doesn't seem incompatible with this plan, but I think the plan is uncertain enough at the moment that it's not obvious exactly what should be done or how things will interact, so things are a bit stalled, and I'm not sure whether anyone is working on firming up that plan (cc @jack).