I don't think the hardware will be fast enough for GBA emulation without serious optimization. Also just wondering, does the GBA run code directly from the cartridge ROM or does it load it into RAM? A GBC emulator will be fully functional with color though
The GBA runs code from the cartridge, unless it gets manually copied to RAM (which many games will do for speed-critical code because the RAM is faster). Of course, most emulators would load it into RAM and treat it as ROM.