The way I see it, we already have 4 newcomers, and there's still quite some time til the game comes out.
While I don't think we'll get as many newcomers as we got from Brawl, I still believe that Sakurai, the man who likes to keep surprises and isn't making another SSE because cutscene sharing makes him sad, would not show his entire hand this early, especially with a potential for another E3 before the game comes out.
I think a lot of people here just are expecting something small so when something big happens, they get surprised, like Rosalina. I myself see the roster growing quite a bit from this game, and would be honestly surprised if we don't hit at least 45 characters, margin for cuts included.