I've seen comments that there might be a different variation of Gear 4th.
First, Bound Man......and then maybe a "Slim Man" mode? That would be be badass.
Not sure I want a slim, super-powered luffy. I'm quite happy with his gear 4th. Moving forward, it'd be nice if he combined all 3 gears, like he was combining the first two. No need to call it gear 5th, I don't think. Just add jet-gigant before each move.
I wonder if 4th has a side-effect like 3rd did, initially.