I think that there are enough spellings out there right now, that it wouldn't always be
Madelyn. My cousin's daughter is
Madeline. But all of them seem to be
Maddy/
Maddie, so some might even assume the full name is
Madison. (I do know a
Madison who goes by
Maddy.) All of them are in elementary school, so it's hard to think of them as
Madeline/
Madelyn/
Madeleine or however they spell it.