> Especially when there are some conflicting reports out there i.e. there are many super-awesome libraries that only work with nightly (I think it's called), because many of those maintainers are early adopters that love to try out new features.

This is totally orthogonal to whether or not Rust stable is backward compatible, which it is. People put a lot of work into making sure it is, and this sort of FUD is very frustrating to read.