Recently I’ve seen an article, “Improving Typ e class Relations by Being Open”, by Guido Martínez et al.:
While it’s about Haskell, I think the same ideas could be adapted to Rust traits.
It introduces class morphisms, with a Haskell syntax like:
class morphism Enum -> Eq where x == y = fromEnum x == fromEnum y
The article lists some disadvantages and troubles with this idea, but in the whole it looks nice.