Gba and SNES emulator on windows phone 8 works fine. I dont think that the problem is the os, the problem is developers who don't love windows phone (why ? i don't know).
I think it's possible to do a fpsce app on windows phone because there's some emulator app (gb,nes, sms).
If the creator of emulator read this, please port fpsce on windows phone!!! we are ready to put money on the table for release this.