I would also like to add an External GPU. (EGPU) This would allow me to run newer generation games. (PS3 and Xbox 360 games and some PS4 and Xbox One games.) MacBook Pro although expensive come default with a virtually no advantage on the gaming side so this would improve my Mac greatly. I have an NVIDIA 550 Ti that I plan to move over to my Mac once I upgrade the card in my desktop computer. I also found lights that from Adafruit that I would like to line the inside of my box with to add to improve aesthetics.
INVIDA 550 Ti: