Final form Imu could be him fighting in Marijoa while sacrificing all the Holy Knights and Gorosei to mobilize the power within himself. On the one hand it's true that Imu already shows most of what he is capable of. On the other hand it would be a lame downfall of the 800 year old King who outlived Joyboy and Davy Jones, to fall in Elbaf while on borrowed time.
