Sure, but bumping the minimum version of a compiler is a way different thing than taking in a new version of a language. Rust will involve a lot of the later, which is bad for the kernel IMO.
The list of backwards incompatibilities in the 2021 edition was pretty small.
I don't think that there will be a need to migrate language versions all that often, and, based on what I've seen of how Rust handles backwards compatibility, I don't think it will be an especially big leap.
I would normally agree with this, but Rust for Linux project in fact uses lots of unstable Rust features, and unstable Rust features in fact break a lot (as they should). Unstable Rust is in fact more painful than GCC C, so pain of upgrade is a genuine con against Rust. I just think benefit is larger.
Will changes to interfaces in nightly be handled similarly to how internal kernel API changes are handled? - i.e. if your code is in-tree then the mantainers of the Rust integration will update your code to ensure compatibility with the new nightly interface.
You don't need to switch editions, new language feature generally are available in old editions too. For example, generic associated types, which came out two weeks ago, work fine in edition 2015.
> upgrading to a new edition of C OR version of gcc
the latter absolutely does happen every few years. Maybe I shouldn't have lumped the C thing in with it, but whatever.