I used the MorphGear GBA emulator and it was hideous slow even on an XScale processor at approximately 700 MHz (usually 624.) I could achieve rarely over 10 FPS. (Bear in mind the performance of a 700 MHz XScale is approximately that of a 300 MHz 'true' ARM9.) It did appear to utilize a C processor core for the ARM7 emulation, and that's going to be the real problem to overcome. A 16 MHz 32-bit processor like the ARM7 is stressful as hell to emulate even on a 200-300 MHz ARM920T like that in the GP2X. I have a strong feeling that project for the GP32 that involved running the GBA's ARM7 code natively on the ARM9 processor, then doing things like audio, controls, video (video handling, palettes, scaling, rotation, etc.) emulated. This way the main CPU will not be so overburdened.
That said, if a fast enough ARM7 ASM CPU core is found or created, it is possible to achieve full-speed emulation, concievably. But it does appear unlikely given the amount of stress created on the ARM920T by a 12 MHz 68000 core! Tacking on the GBA's rather robust 2D video subsystem is quite another task to pile on top of it indeed. Perhaps if the ARM940T could be utilized in some helpful manner, it would be a saving grace for such a project.
That said, were this individual to develop a playable GBA emulator for the GP2X using an ARM9 ASM core, interpretation or what have you to achieve acceptable performance, you'd see donation money from me as well.
