My only input is that we have at least 2-3 (depending on whether the

latter two are to be considered separate) hierarchies in want of
refactoring: Functor/Applicative/Monad, Num and friends, and Monoid.
Ideally any solution would "solve the problem" for all of them, but
even if it doesn't (and only solves, say, Monad's case), I think it
should be a requirement that it at least allows for the others to be
solved as well in an incremental fashion afterwards (whether by
'upgrading' the by-then existing feature, or adding a new, orthogonal
one). The undesirable scenario would be where you would have to
"change the world" all over again a second time to resolve the
remaining problems.