There is another aspect to this: How do you get maintainers to apply the patches? How should hackage be changed to accomodate large-scale refactorings?
There was a discussion on this mailing list related to build regressions on GHC 7.6 last year.
All of the regressions could be fixed using perl regexps, and it was only a few hours of work, much less than the work involved in the discussion itself. I downloaded all of hackage and did the fixes using perl.
http://www.haskell.org/pipermail/haskell-cafe/2012-August/103155.htmlHowever, without the community infrastructure to actually apply the patches, the problem is not solved.
I think this is mainly a community/organizational issue. Refactoring is not really the problem, but of course better refactoring abilities are good.
Alexander