Thinking about this I've convinced myself that what will happen is the ARM core will periodically check for various statuses (i.e. connect to your imap/pop server and see if there is new mail) and turn on an indicator or perhaps wake the intel cores. Which is to say that the powernap/low power functionality will be restricted to either things apple delivers ootb or to a special API. Not as something that automatically migrates whatever workload is running on the powerful intel cores into a slow motion version of the same thing running on the ARM cores.
