Should be helpful in less optimized games. I'm playing Wolfeisntien The New Order PS4, and have read articles that with XB1 and PC there is more noticeable pop in than in the PS4's version. So the PS4 is already quite optimized if it can best pop-in on XB1 and PC. Now engines on other games could have a more severe effect.
My guess is the GDDR5 on PS4 limits pop in in-game, that with a faster than 5200RPM stock hard drive can have more benefits on different engines and pop in/loading times. ID tech 5 is used currently in Wolfeisntien The New Order, and upcoming games like The Evil Within and DOOM 4. This engine is fantastic (can hit 60fps with ease on PS4 apparently) for console games imho.
The only problem with SSD will always be the price factor.
http://www.eurogamer.net/articles/digitalfoundry-2014-wolfenstein-new-order-performance-analysis
