Our events usually start a couple of days in advance and last approx. 1 week after the official celebration day, but there are no strict rules or guidelines and anything can happen.
I can't share many details yet (there's still much preparation to do!), but I will undoubtedly try to send you all on some form of an Easter egg hunt.
Traditionally we do have rewards involved, with Unobtainium being among them, but I don't think I'll introduce any new leaderboards for the event (as you've pointed out yourself, the iOS players miss out on those and I don't want that to happen).