This amounts to enabling PolyKinds in GHC.Generics. However, explicit
kind signatures must be applied to the datatypes and typeclasses in
GHC.Generics to ensure that the Core which TcGenGenerics generates
is properly kinded.
Several of the typeclasses in GHC.Generics could be poly-kinded, but
this differential does not attempt to address this, since D493 already