p.s. -- the only issue I can think of is that it's a little slow, so diff-mode normally only refines hunks when you "visit" them (with n or p keys etc). But maybe magit could just do the same (it seems a little ugly to _leave_ hunks with a different appearance after visiting, ... though maybe useful).
-miles -- Zeal, n. A certain nervous disorder afflicting the young and inexperienced.
