Private lifetime inference

It sounds to me like your biggest problem is having to update a bunch of item signatures whenever you change the lifetime annotations on a type. I think it'd be better to resolve that pain point by adding better tooling (could rust analyzer get an action to add/remove a lifetime annotation for an item?), not by changing the actual language itself. I like having item signatures be fully explicit for reading existing code, even when it's not a public API it helps me quickly understand what the code does.