Maybe, but there are two issues that would need to be resolved. First, Zoro and Sanji would need to fight someone on Kaido's level to equal what Yamato has done and I'm not sure how they could do that. Secondly, they'd have to master using CoC in their attacks like Yamato. Zoro has shown a flash of using it without knowledge of what he actually did and Sanji still hasn't been shown with CoC. That's a lot for them to accomplish just to be on par with Yamato, much less surpass Yamato.
I feel like as long as Yamato doesn't start splitting the sky in half when he attacks another CoC user in the future all of that will be a bunch of variables under that bar. They'll have the time to reach that level.
Given how much story we have left and that Zoro is going to earn the title of world's greatest swordsman I'm not sure its a big issue at all given the remaining enemies and obstacles.
@Shiebs:
Is Kuma completely off the table?
He has interesting devil fruit that fits the 2.9 theory, He definitely needs saving and the Straw Hats owe him one, he definitely has a sad past
Main problem is he’s gigantic, like 25 feet tall, but maybe Vegapunk can upload his consciousness and powers into a new body, seeing as how he has waaaaaaay to many identical clones already that would seem ideal to the character
I don't think Kuma was really ever on the table.
Especially after Jimbe became a friend, ally, and now nakama. As far as the rep of the strawhats or Luffy having a former warlord on the crew I think that stops at 1. The rest will just be allies; Law, Buggy, Hancock, Croc, maybe Moria, probably Kuma.
As far as a new body or being saved, I'm not sure about that. Yeah the crew owes Kuma but it may just be one of those debts that never get repaid (like with Bentham) or they have to pay it forward to someone inheriting his will or something like that.
I kinda feel like Kuma went in to his deals and decisions knowing the consequences and the strawhats can't really do anything about what has been done. Even the speculation about him getting a new body has to do with Vegapunk being the key person since none of the strawhats are experts in that.