My FOGS (favorite online game store) has an interesting entry in their catalog for this year, though it's probably not for 4e and it's not on Amazon or WotC's product catalog: Forgotten Realms 25th Ann. Edition
If done well, this could be really cool! I hope this rumor turns out to be truth. Seems too late for 4E, but too early for 5E . . . but a Realms setting book could easily just skip the rules bits as the D&D core rules cover it pretty well. I think the only thing 4E Realms introduced to the game was the Swordmage/Bladesinger and Genasi, both of which "should" have been in the core rules anyway. Not sure that anything truly Realms-specific was introduced in 3E either, except perhaps the backgrounds (which could have/"should" have been a magazine article instead).