I don't see what Civ V could possible including other than better graphics and perhaps more civilisations?
Maybe this actually IS Civ V. Perhaps Firaxis's whole plan was to release the barebones essentials as Civ 4 and then have Civ 5 simply be the entirety of the mod community. Why do the work when you can have hundreds of people do it better and for free?
Civ6, then.
Come on, you figure firaxis is just going to drop its flagship series or fall off the face of the . .. .. .. .ing earth?