Similar but not exactly the same as named impls, I'd really like to see a language handle this by separating implementing a trait from making a particular existing implementation the implicit default. Orphan rules can apply to the latter, but can be overriden in a local scope by any choice of implementation.

This is largely based on a paper I read a long time ago on how one might build a typeclass/trait system on top of an ML-style module system. But, I suspect such a setup can be beneficial even without the full module system.