The fanbase would be pretty pissed if we had to pay to get a pokemon. Considering that over here in the states we already have a crappy enough of a chance of getting some of these pokes already... (Mew, Celebi, Jirachi, Deoxys, Arceus, Shaymin, Genesect, and Meloetta?)
There's no way they are going to ask for money for these pocket monsters. That'd be awful.
Issue that arise with DLC, is now you are facing some one who doesn't have that DLC. So what happens? Just putting that out there. Though the use of a linking patch (like the berry patch and the bonus Colosseum disc) might make it possible, but with the idea of a whole 3D model, stats and pokedex info seems a lot more of an issue than fixing something with Berries.
[::[_]::]Common sense [+[_]::]just because you can doesn't mean you should