No chance this thing supports carbon, and it certainly won't be x86. At a minimum a recompile, and more likely a complete re-write of apps like photoshop.
Yes, Photoshop is probably the worse example to use as it is Carbon not Cocoa. Adobe are porting Photoshop to Cocoa for the 64 bit support but it is not yet ready.
It is not especially difficult to port apps written in Cocoa for the Mac to Cocoa Touch for the iPhone (and presumably the iSlate as well). The problem with the iPhone is the screen is so small that you need to rework the entire UI of your apps. A single screen on the Mac might need to be multiple screens on the iPhone. That is much more time consuming. However, if the iSlate has a 10" this is much less of a problem.
At the end of the day, I think we will see some quite advanced apps written for the iSlate. Using an OS similar to the iPhone rather than the Mac will not limit the iSlate.