KOF is a crossover itself. I think it has a great formula, FF and AoF chars along with new ones or others from others games like Psycho Soldiers or Ikari. SNK doesn't need SF to rise their series, they only need money to promote the game, a good international marketing manager who knows well international market and continue impoving KOF series from this starting point called KOF XIII.
I don't want to sound like a fanboy...but I think KOF just need to keep the way it has and continue growing and improving.
New story , new characters, returning classic characters or characters who never made the cut in KOF (like Hwa). Try to get close to 2k2UM in terms of number of characters and number of moves, new system (maybe come back to tag combos like kof2003), more balance, espectacular 2D anime cinematics (like story cuts in XIII) for story mode and endings, great online, MazCat official sticks, EVo, Tougeki, t-shirts, corn-flakes, girls cosplaying Mai at every event... And KOF will become hard competence for SF.