So take it how you want it but according to SuperBot in an interview video with GameSpot, there are only 20 main characters in this game... Meaning that everyone has been revealed. The video can be found here.
I'm going to assume this means that the twenty characters revealed will all have full story modes and what not... Any remaining characters would work as unlockable / hidden ones that probably won't have a story mode and just be in Online / Versus.
SuperBot has never stated any amount of numbers for the characters either. All that has been "suggested" was that there are more characters. Could simply be another two.
Hello again! Bye again!