Hermes Serpent wrote: a setting book covering the Blue Mountains might be something in the future. The Shire and Bree are, I think, more likely to be out before anything covering Gondor and I expect to see a book covering the Shire in mid 2015 after the Rohan book and the Rohan adventures
A Shire book seems problematic, because it's utterly canonical that nothing really
happens in the Shire. It's a little slice of the English countryside plopped down in Middle-earth. Tolkien hammers on how peaceful, boring, well-ordered, and free of strife it is multiple times. Up until Saruman crashed the joint there hadn't really been anything that could be characterized as conflict there since the Battle of Greenfields, remarkable literally the only battle to be fought in the Shire until the War of the Ring.
So you would basically have a book of just geography and culture, with very little in the way of sources of conflict, which is kind of important in an RPG supplement. Even MERP, who made sourcebooks for
everything (did we really need three entirely separate sourcebooks
just for Mirkwood, you guys?) never did anything with the Shire of the years of the Hobbit and Lord of the Rings.
What seems most likely is a sourcebook for eastern and northern Eriador in general; the area surrounding the Shire. That's the Blue Mountains, the Grey Havens, Annuminas and the Hills of Evendim, the frozen lands of Forochel, the lands between the Greyflood and the Brandywine rivers, Lond Daer, etc. You know, the bits they didn't include in the Rivendell book.
That seems most likely to me, at any rate, although if it had been up to me I'd have at least included Bree was a place you could go with plot hooks in it in the Rivendell book, being as how it is a neutral, well-known, centrally located town ideal for basing your party out of if you're adventuring in Eriador. So, y'know. I may have a different perspective.