If anyone, I'd see Sabo more with Koala. I like their chemistry

and both backgrounds fit !
Sabo and Koala are a lot more probable as a couple, given the interactions we've seen between them.
I'm mostly just presenting an alternative based on a few subjective interpretations:
- Their plots are now intertwined, given how Sabo's being accused of assassinating her father, and that'll eventually be clarified. I think this pretty much garantees that they'll interact with each other.
- Right before the Reverie, we had Cobra pressuring Vivi to take a suitable husband, and I'd find it an ironic twist that she somehow ends up infatuated with a revolutionary, who happens to be a former royal, and the man falsely accused of murdering her own father.
They're both royals who decided to oppose the current government (it seems very likely that Vivi will go down that path), so I'd find it suitable if they end up being the key figures of the political reshaping that'll take place after the current World Government is brought down.
Sabo's the "Flame Emperor", and Vivi's the current "Queen of the country most associated with the Sun".
(I also believe that Oda drew inspiration for Sabo and Vivi from two mythological figures that have a relationship, but this one's probably just me being wrong)