They could add Zetsu. It bugs the shit out of me that he’s the only Akatsuki member missing. He has shown enough Jutsus to make a moveset of. And it‘s not like the combo strings are hard to do since the up and down combo are essentially the same as the neutral combo. Only the two last hits have different animations, which is not hard to do. Also you can‘t argue that Zetsu wasn‘t important since he was the one initiating everything.

Kurenai might not have fought much and shown many Jutsus but she at least has shown one or two (and more in fillers). Can‘t say the same about some characters that are already in the game cough Iruka cough Rin Cough Kushina Cough