The amount of RAM Sony uses could very well be a lot more than 131GBs because Universal Memory may very well replace RAM chips that are used in systems today.
Universal memory would be the evolution of solid state storage and in 3-5 years it could have such fast transfer and access speeds that RAM simply isn't needed anymore, so we could be saying dozens of terabytes worth of storage will also act as your RAM.
Rather than looking at the scaling of dedicated RAM amounts like 16X what we have today, we could see something that completely breaks the generational shift and destroys the past jump in RAM size that Sony decides to use.
Maybe they'll have a multi-layered SOC, with one layer acting as the VRAM, this could be several GBs, with several TB/s of bandwidth, along with much better latency.
Here's some interesting source material:
http://www.zdnet.com/superfast-solid-state-drive-unveiled-7000032295/
http://www.techradar.com/news/computing-components/storage/how-universal-memory-will-replace-dram-flash-and-ssds-1222632#null
