According to The Sneaker magazine April 2010 issue, part of Suzumiya Haruhi light novel volume 10 “The Surprise of Haruhi Suzumiya” will be published in the next issue to be released on April 30th. The last volume “The Dissociation of Haruhi Suzumiya” was published on April 1st, 2007 and the volume 10 was first announced to be released in June 2007. However, the release has been repetitively postponed.
Sources: Scan of The Sneaker, Scan 2
Updated on April 26th
According to The Sneaker Magazine May issue, Tanigawa finished 80% of the next volume The Dissociation of Haruhi Suzumiya. He and the editors plan to release it within this year.
Source: Scan of The Sneaker
