I agree that it can work, but it's used so much in superhero comics that it just becomes a cliche. The problem is that you know that the original person is always going to come back and reclaim their mask, so having someone else take over is usually just a lazy way to not end a comic series while the main character is temporarily dead.
It can work, like when Batman had his back broken by Bane and he had Azrael take over his mantel to keep the symbol alive, then had to take Azrael down himself when he was out of control. I just generally think it's a lazy way for writers to temporarily kill off a key character while still publishing his monthly book.
I also think that, if they do the Civil War arc for the third Captain America, Peter Parker revealing his identity is that much more powerful because of how long he's managed to keep it a secret and how long we've been associated with the character of Peter Parker. It wouldn't be the same with Morales, who would just be a random guy only a portion of the audience would even recognize.
