This to me makes more sense than a simple cloud scd.
NX will have to have a strong cpu, and so far that is the only reliable leak (LCgeek from gaf who has been accurate in past leaks http://neogaf.com/forum/showpost.php?p=200144552) and it may have been improved upon since then.
Polaris 11 with a strong CPU, is 2.5 tf+ to start off and the NX will be very low power consuming = gamecube like in efficiency. Adding the separate SCD (w/own power supply?) will bump it up to maybe double and above, again depending on the cpu.
Now you have a system that caters to the minimum PS4 requirements, and the mid/upper end as well.








