The popular consensus does seem to be Belf/Amani/Scourge as pretty much assured zones, with the fourth one being up for debate.
It depends entirely on if Midnight is going to be a Quel’Thalas expansion or a Northern EK one. If it’s purely Quel’Thalas, then I think it’s reasonable to assume we get a Naga zone. If it’s Northern EK, then we’re very likely getting a Lordaeron zone across the Plaguelands, Tirisfal and possibly Silverpine.
One thing I wouldn’t be totally shocked to see would be some of those themes condensed into one zone. For example, instead of one zone belf, one zone Naga; Eversong Woods is instead a zone that’s comprised of what we expect as well as the Naga storyline + locations. Same again with merging Ghostlands and Amani into one zone. That potentially frees up the possibility of getting the likes of Gilneas, Hinterlands, Hillsbrad, Alterac and Arathi included too.