What if Robert De Niro and Al Pacino switched roles?

They're very similar people. They're both in my opinion the two greatest actors of all time, they're both Italian, they're almost the same age, height and size, they're in lots of the same movies, they have similar styles of acting, they often play similar roles, and they perform them all brilliantly. I think if they switched all their roles, for example if Al Pacino played Travis Bickle and if Robert De Niro played Michael Corleone, they'd both manage to do them all just as well.