It doesn't make any sense to me that the harmony will play supercharger games considering the supercharger is essentially a ram expansion kit. If the harmony includes extra ram, ect. then that might explain why it is so expensive..... myself I would rather have a basic cart for a more affordable price.
I really want to try my hand at doing a XXX in 1 cart for the 2600. There are pcbs for blank carts for under 10 bucks, some with DuPont header pins so then all one would need is an eeprom, a dip switch array and something to program it with (I think an Arduino would work).