I think that the key system is pretty cool. If you have friends locally that play the game then you can exchange keys and problem solved. If you don't then tough luck. I think that it is a convenient way to get gamers to interact with their friends through the game. Or if you have both games and two DS' then you'll be able to exchange keys that way. I think that it would be cool if there was an event with the key to get the other regi, that way this problem could also be solved even easier.
Keys can be transferred to the other games to catch the opposite Regi through Unova Link.