The problem is, BB is aiming for op too. He got the pone rubbings from Law, and Pudding. So he's an active participant in the op race. Right behind luffy.
So i don't think he's just gonna drop out of the op race and bide his time.
That's why i think the BBP vs SHP fight will be at or right before Raftel.
Ancient weapons could come in to play during that too.
Maybe he kidnaps Shirahoshi and threatens the SHP with killing her. And that sparks the fight. Or maybe he takes wano and yamatoe/momo and does the same with pluton.
All in all, i still don't think he's the final villain.