Eh I'm not sure if that's the case. Both the current Starter's Box and the upcoming Essentials box are for FR. Obviously WotC could make another FR box (FR has such a long published history that WotC could launch content for it until the end of time), but it wouldn't add too much incremental value over what already exists for 5e.
I think Lowkey13 is more on the mark about what they're working on. Greyhawk for a boxed set makes complete sense to me for a starter's set, and would be picked up by people who already own the current starter's set but also want Greyhawk 5e content.
I wasn't taking about another starter set, but a full on campaign box set, which is a very different beast from a starter set. Might not have an adventure for example, it'd have updated lore, a big map of Faerun (maybe Toril as a whole), info on various regions, the target audience would be not be newbies (although perhaps it would be presented in a newbie friendly fashion), but rather major fans of FR.
Also remember WotC is hiring consultants on various none European inspired FR cultures.