Or Luffy could have awakened into a mindless ape against Kaido, the arc build around beasts, and only learned to control it with the help of the entire Onigashima, Momo and Yamatoe included, leaving the white form and G5 proper for Elbaf, after the mural.
The ape form could have been a berserk form a la Naruto pre-4 tails, only bringing it up when absolutely necessary.
It would have been a lot funnier, too, to have the Egghead panel with the five demonic Gorosei squaring up to a tiny, dumb-looking ape.