I would also like to see the design of Super Saiyan 4 return, but not with that name. The fact that it's considered a Super Saiyan form despite looking nothing like the others is my main complaint about it. I would really prefer it to be shown as the next stage of the Oozaru branch of abilities. And I'd like for Gohan to figure it out, after what he said about going down a different path than his father. He could think about how Saiyans have both the Super Saiyan branch of transformations and the God branch of them, how they're separate from each other and can be mixed, and wonder about a third branch... and then remember that we already saw a third branch, Oozaru. He goes to Vegeta, asks about how he mastered the form. He gets his tail though a wish or a special Senzu Bean or something and trains in the HTC as Oozaru, mastering the form and beyond, to the point that he achieves a harmony between his Saiyan and Oozaru forms, which is basically SS4 by another name.