So...
Do you think Sakurai will reveal a newcomer outside of a big event like E3 or a direct?
Randomly? I don't think so, we'll most likely see characters without a release-celebration in Directs or at E3, assuming the game isn't released before E3 2014. I.E. Little Mac, Ridley, or Palutena.
Newcomers that have a game coming out may be revealed on the Dojo to celebrate the release of their games. I.E. Bayonetta, King K. Rool, Dixie Kong, or Waddle Dee.
Veterans can pretty much be revealed at anytime Sakurai wants as seen with the Peach reveal, but the majority will most likely be revealed to celebrate the release of a new game. I.E. Olimar (Pikmin 3), Luigi (M&LDT), Toon Link (WWHD), and Sonic (Lost World).
However, this does not mean a character will be revealed for every big release, as seen with no character reveal as celebration for the release of The Wonderful 101 and Pokemon X & Y.