Yes but I'm saying this is kind of moot when you're writing a struct that needs to store the iterators, because it can't get away with just storing the 'begin'

Yes but I'm saying this is kind of moot when you're writing a struct that needs to store the iterators, because it can't get away with just storing the 'begin' -- you can't guarantee the second iterator you're storing will actually be the end. Meaning this iteration model isn't efficiently composable.