First of all, you would probably need more than a PIC12F863, because it only has 6 I/O pins, and to get something bigger to fit into a controller, you would probably need a QFN package or some other small surface mount package. Also, to make a microcontroller compatable with a SD card, now im not sure about this, but i think you need to buy code from the maker to make devices compatible with it, and it would probably be some hardcore programming.
I was thinking about making something like this, but it would just plug in through USB, so using a PIC18F4550 (of cource, a small package to fit inside the controller ), and just storing patterns on the built in EEPROM, but the problem with the EEPROM is you have only like 256 bytes of data to store patterns on. I think this would be a great project for me to attempt, in fact, i already have 2 18F4550s on the way, but i do not have enough hardware knowledge to figure it out. I've tried to get some help, but i cant seem to get much as of now.