rr and Gdb are very DWARF debugging focussed. As long as Haskell has only basic DWARF debugging support I wonder how much rr/gdb can do.

Though I do see a lot of promise in the future. rr can help make premature evaluation (many expressions are evaluated earlier than they might typically happen in a real Haskell program because a user may want to inspect a value) in the debugger not matter so much because that evaluation can be executed in a diversion session.