Nintendo reluctantly started offering for-pay downloadable content. However, the company is adamant customers shouldn't feel like they're buying an incomplete product. While Nintendo has developed interesting add-ons for their franchises, like Pikmin and Mario, its cash cow franchise, Pokemon, is resisting the idea. That includes the imminent releases of Pokemon X and Y.
"There’s no download content or microtransaction content developed specifically for Pokémon X and Y," Game Freak director Junichi Masuda told VG247. "We've not come up with any ideas on that yet. I like the idea that Pokémon can be enjoyed with just one piece of software. You buy the game and it can be enjoyed just with that one software that you buy. That's a key point for Game Freak."
Of course, it's impossible to catch 'em all in any mainline Pokemon game without trading with other players. However, even with Masuda's reservations, Pokemon's collection-based gameplay would seem to lend itself to selling DLC-based monsters.