TypeOperators as a language extension doesn't require a whole lot on the behalf of implementors today. They basically just have to add fixity handling to types. This is a no-brainer for a compiler implementor. It is a simple elaboration and some extra cases to deal with in their parser. The typechecker changes are obvious.
Asking them to do all the things to support 'some typechecking details' that aren't entirely trivial to support that same extension is an awful big ask! OutsideIn(X) is a big paper to read, let alone implement, and the only compiler to even try handling (~) today is GHC.
-Edward