Crossfire on high end cards already is not ideal since it has higher prevalence of micro-stutter compared to SLI due to lack of dedicated hardware frame metering. Crossfire with low-end slow GPUs is going to be stutter-fest galore. They would be better off going with A10 + HD7000/8000 dedicated GPU. The GPU in the APU could be used to power certain indie titles/arcade games that aren't GPU intensive enough, cutting down on power consumption in those titles. It could also accelerate 4K movie playback, etc. allowing the dedicated GPU to go into ZeroCore power savings mode. The dedicated GPU would then be used for next gen 3D games where more power is needed.
Also, if AMD is building them a custom A10 chip, it's not a required assumption that an A10-5800K will be used with outdated VLIW Trinity GPU. AMD already launched 28nm GCN parts in the mobile space and there shouldn't be any reason why Sony won't want at least a GCN GPU inside their APU.
A 384SP GCN mobile part mops the floor with a 480SP VLIW part.
http://techreport.com/rev...ok-at-amd-radeon-hd-8790m
It would be short-sighted at this point to use an A10-5800K.
I think a mobile variant of the desktop HD7850-7870 2GB is the minimum that PS4 needs to drive next gen graphics (so roughly equivalent to an HD7950M for its dedicated GPU). The console has to last 7-8 years from launch, not just be good enough to play 2013 PC games.