We can't accurately judge this that much because we don't know what kind of hype they want to generate. There's far too many angles they could go with this, and of course a few of these have happened before but the thing is that recurring occurences =/= patterns which are not to be broken.
Do they want to appeal to the Japanese, as a sort of bone throw since Western fan favorites have been dominating the roster? We could see Jibanyan, Arle, Bandana Dee.
Another Western fan fave? Isaac, Professor Layton, Rayman.
Do they want to simply show off their impressive rights management? Sora, Banjo & Kazooie.
Do they want to break the rules? Prove the impossible is now possible? (Presumably not because of the outcry, but in the event they did...) Waluigi, Ashley, Goku, Batman.
Hell, it could be somebody lukewarm and underwhelming. Shulk was only really hype if you already wanted him. Olimar is kind of in the same boat from Brawl.