Full x64 ISA and 10.6.
It will most likely be 10.6 (Snow Leopard)... but running on ARM (32-bit) with the Cocoa Touch iPhone GUI on top, and running some form of App store apps.
Tablet PC's are a big fail, so this device, if it exists, will distance itself as far as possible from having any PC or Finder desktop in order to succeed.
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