4 MB is the maximum size of the console's ROM address space, so this would've allowed for any Genesis game to be published through this service, with the except

4 MB is the maximum size of the console's ROM address space, so this would've allowed for any Genesis game to be published through this service, with the exception of the few games that used bank switching to go beyond 4 MB (really only Super Street Fighter II). 4 MB was a lot of RAM to be putting into a relatively cheap consumer electronics device in 1994, so I imagine some of the cost of that was subsidized by Sega and had to be covered by the subscription fees.