What will be the next app after PPSSPP??

[geigermuller]

A psvita or nds3d Xl emulator might not really be worth the trouble since they are much harder to emulate, even ignoring the hardware requirements, and they have a relatively small library of games due to poor sales.

As for a ps2 emulator, it would only be available on mobile at least two years from now. But Sony might release an Xperia Play 2 with emulation support for ps2 games, just like how the current Xperia Play can play ps1 games.