That's disappointing, especially from the lads who gave us that 8 GB GDDR5 shocker haha.
It's possible they can clamshell the memory and ship with more than > 16GB, but it'll be a waste of money as SSD already increases effective memory by a magnitude over current gent.
Consider a 30 second game loop.
Current gen: 5GB + 30 x 50MBs = 6.5GB
Next gen: 13GB + 30 x 2GBs = 73GB
More than 10x effective memory in a 30 game time slice.