>>13I don' think it broke anything. Many Prelude functions that used to only work on lists now work on Foldable. Now List is an instance of Foldable, so those same functions still work when applied to lists, in addition to anything else implementing Foldable.
The only downside is less discoverability for those particular functions. Not that discoverability wasn't a problem before - many libraries I have tried to use have data structures that implement about fourteen thousand interfaces, which causes the same "so what the fuck can I actually do with this?" problem as inheritance in OOP, but an order of magnitude worse.