DEFINITE: OGL (Mearls said); Elemental Evil story arc (announced months ago)
PROBABLE: a third story arc in the Fall (they've variously said "one or two a year")
POSSIBLE: Forgotten Realms book or box (I'd say probable because they really *should* release this, but you never know); online Dragon and/or Dungeon (who knows - I think we'll see something, but maybe not what we've had in the past); some minor Winter release to tide things over between the Fall and Spring releases
UNLIKELY: Anything "2" (PHB, etc - just too soon based upon their stated release strategy); Manual of the Planes (too soon); a new or different setting other than the FR (will need to do FR first).
I maintain that we're going to see a continuation of the following release schedule:
Spring: story arc (two books)
Summer (GenCon): major release (campaign book, big splat)
Fall: story arc (two books or box)
Winter: minor release (e.g. DM's screen, a supplement of some kind)
Seems sparse, but that's what they're going for. Alternately I could see that winter release being larger, similar to summer but less publicized.
I'm hoping that one of these story arcs is actually a sandbox box set ala the Wilderlands of High Fantasy, but perhaps in Greyhawk and doubling as a campaign sourcebook. Imagine that: a Greyhawk box set with a world book and detailed hexcrawling in the Greyhawk environs region. Grognards everywhere would rejoice and experience hopefully minor heart palpatations. Maybe 2016? On the other hand, they could release it in 2015 as a 40th anniversary to the release of the original Greyhawk pamphlet.