You know, I've been wondering this myself and we talk about "Forgotten" classes - but it seems to me that Eberron is the forgotten campaign setting. Dark Sun and even FR are seeing regular support (well FR is getting an entire new book) in Dungeon/Dragon (at times). I can't recall when something for Eberron was published since Q'Barra last year and what (if anything) is coming for the setting. Coincidentally, some of the most poorly supported elements in 4E: Changeling and Artificer are both from Eberron originally.Of all monster races, I think the most overdue are goblins/hobgoblins, if only for the fact that they play such a large role in Eberron.
I cannot help but notice that.