The current limit is 1gbit with the technology allowed, but as with as far back as Nintendo's 8bit roots you can do stuff like they did in the day (bankswitching on NES carts) to allow for larger cart sizes that do more than the original hardware could allow for. Every cart (or in the case of DS ...card...) system made by Nintendo to date has always had a game that has gone beyond the specs due to bankswitching, new hardware, new techniques...whatever (Virtual Boy aside as it petered out.) GB itself should have done I think just 4MByte carts but Densha de Go did 8MB over there, and like the N64 didn't get larger but got new chips to allow for new stuff as did the SNES...MPEG chip (re4, pokemon puzzle league) and FX chip and about 12 others on the SNES.