Amazon is no longer selling the Kindle DX, and based on their general disinterest in updating the hardware or software, I don't expect it to come back into stock. This ereader was released in 2009, updated in 2010, and then basically ignored since then. After the price cut a few weeks ago, and now an OOS message (with no expected return date), it looks like this ereader is no longer going to be available.
Amazon first unveiled the Kndle DX in June 2009, making this 9.7" ereader the third Kindle released as well as Amazon's first large screen model. This was the ereader which Amazon expected to be adopted as a textbook platform. And in order to promote that goal, Amazon also announced that June that several major US universities were going to run pilot programs using the Kindle DX in the classroom.
Yeah, that didn't turn out well. Amazon learned the hard way that when you pitch a product for the student market one, it needs to be usable by the visually impaired, and two, it needs to actually function adequately at its intended purpose. The Kindle DX failed on both counts.
Several lawsuits were filed in late 2009 by visually impaired students and the National Federation for the Blind. In general, the universities were faulted for failing to comply with the Americans with Disabilities Act. This law specified that the disabled students were to be given equal access, and that has long been interpreted both by the NFB, the Dept of Justice, and quite a few judges to mean that schools and institutions can't buy radical new tech if the visually impaired cannot use it. This interpretation of the ADA has long been a thorn in the side of ereader makers and it is still tripping them up. Witness the recent settlement by the Sacramento Public Library as an example of the law being enforced, and the K3 (Kindle Keyboard) as evidence of Amazon's response to the lawsuits in 2009 (that ereader is ADA compliant).
But even if the Kindle DX had been accessible for the visually impaired, it was still not all that usable as a textbook carrying ereader. The several partner universities released reports in 2010 on their various pilot programs, and for the most part students didn't care to use the device.
Universities as diverse as Reed College, UVA, and (as well as several later pilots like the one at the University of Washington) all reported that students didn't care to use their digital textbooks on the Kindle DX. Leaving aside the difficulty in getting the text into the Kindle format so it could be used on the KDX (this isn't nearly as much trouble now), many students found the Kindle DX generally slow to respond as well as not terribly comfortable to use.
Students commonly needed to make a lot of annotations and then access them quickly and the KDX simply couldn't match the speed of a student with a pen in their hand. The students who participated in the pilot programs also reported that the Kindle DX couldn't turn the page fast enough nor jump around inside a textbook as quickly as they needed. And then there's the issue of having only one screen to display several textbooks for a course, but that is a problem all ereader share.
All in all, the Kindle DX turned out not to be nearly as useful as the 6" Kindle, but I suspect it was more successful than we might think - at least, Amazon sold enough units to justify an update in 2010 and continuing to keep it in stock.
Given that this ereader debuted less than a year before the iPad, and yet managed to stick around for 3 years when most every other large screen ereader died in early to mid-2010, Amazon must have done something right.
Nevertheless, I will not mourn the passing of this ereader. I have one and the iPad (or most any Android tablet) is frankly a better value.