I think this sounds very likely. If you have a strong campaign setting with lots of fans, it seems odd not to make this the default setting for your game. The halfway house we had with 4e (and to a lesser extent 3e which used a kind of Greyhawk Lite) doesn't really help anyone.The Forgotten Realms "Sundering" event is going to be pushed hard with the development of DNDNext, as mentioned at last year's GenCon. With the start of Vault of the Dracolich game day event, and upcoming DND Encounters, I'm thinking the default campaign world for adventures may be Forgotten Realms for Next.
The next two Encounters adventures are both FR related, and I can see all foreseeable Encounters adventures being FR focused as they move through the Sundering event leading up to release of DNDNext and beyond to a release of a FR campaign book with all the updates.
I don't think this will become Next's Sunless Citadel though, due to its limited distribution.