My instinctual guess would be it's just "ubuntu with unity by default" just like traditional ubuntu installations, which you could swap out for any of the other interfaces. That's one of their key features after all.
This is only inferred from what I've read and not based on any specific statement from canonical.
After further review, seeing as this will have the software center built in, I am now wondering if you can just apt-get install kubuntu-desktop and such. Maybe one of these days they will release it to the masses. If they do, probably after the conference coming up.