expr.try still only talks about being applicable to Result and Option, and describes its behavior as if hard-coded for those two types. While Try/FromResidual are still unstable, they are already implemented for other stable types - namely, std::ops::ControlFlow and std::task::Poll - and the trait methods are already usable within stable Rust through the ? operator.

I think it would be nice for the reference to acknowledge this progress now. While the API is in a half-unstable state, and there are still unresolved issues in the tracking issue, the operator is no longer hardcoded for just Option and Result - it might at least be worth it to reference the two other implementor types.