I'm even more surprised that there is a working PSP emulator for Android. I never knew there was such thing, I'm about to buy an Xperia play but these emulators probably run like shit on it cause its single core.
Yeah PPSSPP is really impressive. I guess it was always in the realm of possibilities since the PS Vita apparently uses emulation to play PSP games. Vita after all has somewhat comparable specs to modern phones and tablets (similar CPU and GPU architecture) and it doesn't have PSP hardware or native back compatibility built in (unlike how 3DS is natively back compatible with DS games).
I doubt you'll have much luck running PPSSPP on an Xperia Play well enough (even the best phones still struggle with it). DraStic on the other hand actually seems to run shockingly well on the Xperia Play given that it's now really old hardware. Some of the more intensive games may require a bit of frameskip, but many games actually look like they're running very fast and smooth. I guess it depends on the game you play, but there's a guy on youtube called FeanorBR that has been testing a number of DS games on the emulator using an Xperia Play. Even some of the more impressive 3D games such as Dragon Quest Monsters Joker 2 are running really smoothly. Mario Kart DS seems to be one of the more intensive DS games to get running but with some moderate frameskipping, even it looks to be entirely playable. You can check that guy's channel yourself, he's uploaded quite a few videos of DS games running on Xperia Play. He did overclock his to 1.6ghz though.