Right now, DLC is still being considered as a possibility.
Yes, there's Mewtwo. But that's all there is at the moment. It seemed to me that Sakurai has a bit of an open mind towards DLC, but is being cautious towards it. Doing DLC is an investment in time, money and manpower and that effort can't go to waste. It has to be profitable and worth the hard work.
Sakurai has already done a full package of content without prospect of adding more to it, which is a good philosophy. He ensured to deliver a product as complete as possible, unlike certain companies with their dubious practices of releasing blatantly incomplete games and use DLC to fix stuff or having DLC pre-installed in the disc with the fee merely unlocking said content.
Mewtwo is testing the waters for a series first, so the best we can do as fans is to support the game on the long run. Do you want more content added to the game? Do you care about the game? Do you want to give Nintendo and Sakurai a reason for why DLC should be a thing? Download Mewtwo. The more people do it, the better the chances for more DLC. Right now, it's up to us. It's in our hands.
Even if you don't care about Mewtwo, don't like the character, are not a Pokémon fan, download him anyway. He shouldn't be too expensive either, but that money will add to a total summed up by all Smash players. Pokémon has one of the biggest fanbases and is a powerful marketable brand, so Mewtwo is a very wise choice when it comes to test the waters for further DLC. Add the fact he had been playable in Melee and said choice becomes even wiser.
Now, it's up to the fans. I think the best Wolf fans can do now is to support the game as is. Try to get both versions and even if you can't do so, download Mewtwo when he becomes available to everyone (after the promotional period).