Something I've been hoping for for awhile now would be like a guaranteed death type move. Kind of like a "fatality", but less generic. Like 410 blowing up the oponents heart, Battler's blue truth spires impaling, Shannon creating a cylinder shield that crushes the enemy against the wall, or Ange denies the enemy's existence. Kind of like how in BlazBlue there are two hyper combos, and then when certain conditions are met you can do a hyper finish.
Clearly I would be fine if the next OMK didn't add any characters so long as they balance everything and add more moves.
Reguarding new characters though, it looks like they're trying to focus more on the important characters as well as the popularity poll, so they'd wait awhile before touching characters like Gaap, or Ghoda since they aren't as important storywise. Now that they've taken care of the Chiru characters, we'll hopefully start seeing more minor characters in the future!