I've been going a little crazy these past few days trying to find out when the 10th Haruhi novel is coming out. So far, no hard date. There's some news from last summer about it being delayed. This thing (described as a shareholder report by Babelfish) shows 涼宮ハルヒの驚愕 due sometime this month. However, given that there's been no massive ad campaign, it can't be arriving anytime soon.
I kind of feel that Tanigawa-sensei has written himself into a hole with the plot direction in #9. From past author's notes, Tanigawa-sensei gives the impression that he spends a lot of time in plotting and planning. Since #10 is supposed to be the conclusion of the arc started in #9, the only thing that could be holding it back so long is a massive replumbing job. At least that's my hope. #9 gets into dangerous territory, in that it focuses the overarching plot, introducing new characters and potentially expanding the SOS-dan. In previous novels we've spent a lot of time delving into things involving Yuki and Mikuru, and not so much the Haruhi=God supposition. By extension, we've yet to see much of Koizumi's secrets. I doubt this forthcoming novel will blow the whole thing wide open, but hopefully it'll answer more questions than it raises, without sinking the enterprise.