Seeing how the cover for Volume 69 is out now, we can start predicting for this one now. Though I wonder if with the latest volume postboned, we will get this one in 3 or in 2 months now.
Name: "Matching Interests" or "Leave it up to me!"
Characters: Luffy, Doflamingo, Caesar, Buffalo, Baby 5 & maybe Kuzan (+Usopp and/or General Franky as additional Strawhats)
we'll get a reverse cover of Volume 69, with the title being "Smile" (which would be one of the next two chapters). Doflamingo would be in Law's position, Caesar in Luffy's, Baby 5 & Buffalo in Chopper & Mocha's, Vergo & Monet ready to die in Zoro & Tashigi's and Kuzan in Smoker's.
That would at least excuse that some significant characters were excluded on the latest cover.
Also Smoker, there can't be a volume cover without Smoker anymore.