I'm combing for those rumors, but they're just not out there in any trustable or meaningful way. It is getting close to when we think the selection of OEM will be made and when supply chain rumors start developing, but it's really possible Google already selected a manufacturer.
As far as specs go, it's a little hard to be worried, given that every Nexus device thus far has been at the top of the spec race on it's release day for it's niche. I think we can make some assumptions, but doing so this early is really just a guess based on the last one. I think it's safe to say based on the GE phones that it'll be GSM only with AT&T and T-Mobile LTE (possibly), and that we probably will not see a CDMA version again. I'd assume we see a 16GB version and either an 8GB or 32GB version for $50 less or more, respectively, depending on how sales of the 8GB N4 went.
As for the next version of Android: The extra sensory API's discussed at IO on June 15th, also believed to be loosely described by the Moto X discussion, lend credence to the possibility of those sensors being in the next Nexus, however aside from those and some additional methods or returning power to Google regarding functionality fragmentation, I wouldn't expect any major breakthroughs in software. This will be more similar to a 4.2 from 4.1 update, rather than a 4.0 from 2.3 update (or 3.x if you had a tablet or Google TV).
One major rumor about KLP is software optimization on low to mid-range hardware. This lends to two ideas... one, the overwhelming consensus among nerds that we're not using the majority of the power offered by the high end specs on flagship devices and two, that because of one, it's possible that Google will be pushing to have a much higher quality user experience on much cheaper devices, thus allowing them to push their dream of more access to the internet and related services on a much more global scale. This is also in line with Motorola's comments about the prices of smart-phones, as well as those of Larry Page in his speech at IO.