They could hold the sav data for 2 carts inside a the ram expansion pak, maybe, like, "insert cart 2 now", then it loads, continue the game. It did say that the mem expansion pak only works for compatible games in the opera manual, and there has only been one game for it. There should be more games taking advantage of the extra ram in my opinion. Better graphics from games, more save slots, etc.
It's IMPOSSIBLE for Nintendo to allow a game to be released on two cards.
Reason: open any DS game manual and read the instructions: NEVER REMOVE THE DS CART WHILE THE POWER IS ON.
That's a Nintendo requirement and they're not going to change it just for DQ9, even if they're probably more than happy to have the title on their console. It could harm the console as well.