I don't see much gain. It will break previously working code and the workaround to the breakage will likely be manually reimplementing enumFromTo in each instance.
As an aside, many years ago I did exactly that after being bit by Enum infelicities, and while you could say it's a reimplementation, in my opinion it's a better implementation: -- | Enumerate an inclusive range. Uses multiplication instead of successive -- addition to avoid loss of precision. -- -- Also it doesn't require an Enum instance. range :: (Num a, Ord a) => a -> a -> a -> [a] range start end step = go 0 where go i | step >= 0 && val > end = [] | step < 0 && val < end = [] | otherwise = val : go (i+1) where val = start + (i*step) -- | Enumerate a half-open range. range' :: (Num a, Ord a) => a -> a -> a -> [a] range' start end step = go 0 where go i | step >= 0 && val >= end = [] | step < 0 && val <= end = [] | otherwise = val : go (i+1) where val = start + (i*step) -- | Infinite range. range_ :: (Num a) => a -> a -> [a] range_ start step = go 0 where go i = start + (i*step) : go (i+1)