If it would be possible, it'd be released already in retroarch for the 3DS. CPS1 and CPS2 are using the same processors, the later CPS2 just at higher frequencies (main CPU Motorola 68000 at 10MHz and 16MHz respectively). CPS3 uses a different set of processors, not compatible with the predecessors (Hitachi HD6417099 (SH-2) at 25 MHz). So I think the 3DS isn't powerfull enough to emulate this system at full framerate. I'm guessing because of that team libretro could have dropped it.