The original FPGA wasn't strong enough to combine RedGuy's SA-1 with the MSU1. From the sound of it, this one is.
If I ever got around to making the Super Accelerator F-Zero game I've talked about (I won't), that combination would come in handy.
I don't know why you'd ever want to replace the music in Super Mario RPG. Except the battle music. The battle music kinda sucked.
[EDIT: According to
this video, the new FPGA does indeed allow SA-1+MSU1. Works out of the box, according to ikari. ST-011 in future plans, possible Super Game Boy (blue sky). Still no ST-018.]