I saw the top and the moment I scrolled I legit thought of that scene from Incredibles haha- but I think this would be a horrible idea. Normally I'd make an analogy but I can't, so I'll just flat out say: That quote says it all, "When everyone is super... no one will be." It's the irony of this whole question and the ideology behind birthdays that make them special. Birthdays, and from what I also tend to hear, Special Days, are well, special. If everyone were to celebrate it on the same day then no one would be special in a sense and it would be more of a mandatory thing than a surprise or loving event.