Enum k => EnumMap k v as generatisation of IntMap v ?

Sometimes I want `IntMap` performance, but `Enum k` typing for more expressive source code.

This can be done with a heap of boilerplate code: https://gitlab.imn.htwk-leipzig.de/waldmann/pure-matchbox/blob/master/src/Matchbox/Map.hs - and I hope that ghc will make sure it has no run-time cost.

Could (something like) this become part of containers?

Or does this have a totally different solution (with associated types perhaps) that should not be part of containers?