Some of the features of PS Touch are being able to insert a camera layer or use the "camera fill" feature, which might be a little tricky considering the Nexus 7 only has a front-facing camera. (One could, of course, use its Bluetooth to transfer photos from another device with a camera.)
I talked with John Nack via email from Adobe Blogs: http://blogs.adobe.com/jnack
Apparently Photoshop touch works in Android 4.0 IceCream Sandwhich, there is no reason (that anyone can give me) that Photoshop Touch or any of the other Adobe Touch Apps shouldn't work in Nexus7. I feel that Nexus7 actually should be perfect for them given the RAM and NVIDIA Graphics, not to mention the processing power.
I actually cover my thoughts concerning how the Google Nexus 7 will effect the design landscape in general here:
With the sellout rate Google has currently for these tablets theire can be no doubt that it will be supported, Furthermore with Apple set to deliver and iPad mini before the holidays, you can bet that Adobe is hard at work enhancing an update for these apps to fit the 7inch platform.
We've just released PS Touch 1.4.1, it should then be possible for you to use it on the Nexus 7.