I feel like that might leave embedded devices without an upgrade path, and those are the devices that needs to longest "warning". So yes, borrowed time, but that might be a decade.

That no to say that Rust shouldn't be considered, but maybe initially for new development or selective rewrites. Some of the mentioned, like nscd or devd in particular, shouldn't be that high on the list. The ZFSd should be fairly safe, as that's mainly needed on the larger platforms.