I'm not so optimistic. When they're charging $20 extra for 3 "city sets" I don't think EA will want to eat into their DLC profits by allowing people to create their own versions of these pricey sets. Maybe they'll set up something similar to an app store where you can charge money for a mod you create and they take a cut, only allowing the mods that they approve. I don't envision them allowing anyone to create anything and distribute it anywhere for free. I trust that Maxis sees the importance of the modding community but I don't trust EA at all.