I'm sure a PS2 emulator has novelty value but I'm not sure many people will really be that interested. Wouldn't a PS3 emulator make more sense given a lot of PS4 owners may still have a PS3 to play PS3 games and might prefer one console to do both? Or is the PS4 simply not powerful enough to do it?
Sony's solution is Playstation NOW. It is a streaming service to let you play PS4 games on your PS4 using a streaming "rental" model. The plan is to include PS3 games at some point.