Oo yay! Arbitrary speculation! My favorite kind!
Lessee...since they've been consistently clear that FR is going to be their go to setting...I'm thinking something like this...
2014
Forgotten Realms: Tyranny of Dragons
Greyhawk: Elemental Evil
2015
Forgotten Realms: Drizzt! Gesundheit.
Ravenloft: The Vampire Trolls for Thee...(the "and here's how inter-/para-/demi-dimensional stuff can be used" adventure path)
2016
Eberron: Ridden Out on a Lightning Rail (the "you've been screaming for 'em for 2 years, now lookit this: a whole world with Magic Items EVERYwhere!!! Aren't we great? Don't you love us?" adventure path)
Dragonlance: Lance? We don' need no stickin' Lance.
2017
Forgotten Realms: Realmsy Realmsington (the Forgotten Realms are baaaack adventure path)
Greyhawk: Descent to the Depths of Tsojcanth a.k.a. "Grazzt! Gesundheit." (with great marketing fanfare and buildup for the "long awaited classic(s)", since you haven't seen GH material in the last 3 years since 5e's release)
2018
Forgotten Realms: Happily Ever Elminster
Second adventure for whichever proves the best received/most popular: Ravenloft, Eberron or Dragonlance.
Planescape [re]introduced in there, probably 2015, as a Manual of the Planes type setting book, probably with some small adventure in it, no adventure series.
Kara-Tur [re]introduced in there, probably 2016 if there's enough call, as setting book, probably with some small adventure in it, no adventure series.
Birthright, if comes up at all, in a kingdoms/mass combat options book, probably with some small adventure in it, no adventure series.
Spelljammer...if you see it at all, elements of it could be incorporated into the PS setting book..."jamming" across the Astral Sea and such.
Mystara...I'll be very surprised to see them use Mystara as a stand alone setting for 5e when they already have FR and GH.