Luffy vs Akainu is the most likely out of all of em' by far.
Akainu fighting Dragon to some capacity is pretty likely as well, but absolutely not guaranteed. It'd be a real shame if Oda doesn't bring this match-up to the pages. It's got so much potential.
Akainu having some sort of skirmish with Sabo isn't unlikely, but it won't be Sabo's final fight, that's fairly obvious. His main targets are the celestial dragon scum, that's been reinforced several times within the story. So I do think Oda may have them clash for a little bit to show that Sabo has definitely surpassed Ace, and that his fire isn't smothered as easily, but that's about it.
Dragon vs Warcury is significantly more likely in my mind than Akainu vs Warcury. Warcury's just the perfect hype tool. He's got the best Gorosei feats atm, but his personal role in the story is not nearly as significant as Garling's. Dragon using the dragon claw martial art + ACoC to crack Warcury's fabled defence like an egg and permanently injure him is something I can clearly envision.