I joke about Sanji, but I think Seraphim-Mihawk, or another Seraphim, is going to give Zoro serious trouble.
Zoro hasn't had many L's lately, outside of our own desire for ZKK. It would be ridiculous to have Blackbeard struggle a bit with Seraphim Mihawk, then have Zoro casually beat him up.
The Seraphim are no joke, and will probably decide how this arc goes in terms of who has the upper hand.
If Vegapunk controls the Seraphim, he's safe. If CP0 is capable of turning Seraphim Jinbei and the others against Vegapunk, then this will be a hard escape arc.
Either way, expect more forces, like Cross Guild or some of Blackbeard's 10 Titanic Captains, to show up, to even the playing field.