If Erdrick is going to show up one way or another, I'd rather they be announced later on. How later doesn't matter, as long as we get a character no one is expecting. By that, I mean a character that has earned a "Literally Who" and/or "Never Ever" status. That way, we get something new, different, and surprising within context of speculation. Erdrick would then be expected for E3 or somewhere close and possibly have his/her announcement paired up with an accompanying Fighter's Pass character that we may or may not know about.
Spreading those announcements across and balancing the hype accordingly would make it so that the news droughts aren't as dry as we'd hate. By having Erdrick announced next, it kind of becomes a, "yeah, we knew he was coming" deal as opposed to the more-exciting news that Joker brought with him on the night of Ultimate's release. In short, delaying Erdrick has its worthwhile benefits despite still being expected in the grand scheme of things, because he/she gives another character room in the spotlight for us to discuss both for months to go by.