Keep all new characters, get rid of the two mimics that were nothing more then wasted character slots (only one mimic is needed) and replace them with Zasalamel, Yun-Seong Talim or Seong-Mina. Two of the characters from this list.
If Elysium were to return, give her her own style.
Either make Kilik the new Edgemaster or give him his style back. Personally I really don't care if there are people who use similar weapons.
Give characters their own arcade endings and give people the option of viewing the concept art and character profiles.
And I don't know too much about new characters but I'd love to see Ashlotte back. Best guest character they had so far. And she actually has a plot in the story.