The thing is that if they're going to (G)DDR for main memory, then there has to be a re-working of the architecture on some level, due to the memory controller. If they would actually make that change in isolation to IBM (who would ostensibly benefit also)... I think we'll simply need more clarity as info dribbles out slowly across the months to really understand what is up.
It shouldn't be a huge deal , don't the server cell chips use ddr ram ?
Also a split pool of 512 megs and 2 gigs would work well I'd say for a ps4.