Goofy HAS to be in. He's two-legged, a fan favorite, and he would make an amazing character to play with. Remember those years when he played pretty much every sport. That makes for awesome fighting accessories!
As far as DLC goes, I would assume they could go that route for additionnal content related to figures and playsets not on the game disc. So a playset could be bought in stores like everything else, but would state that it requires an internet connection to be able to download it and play it. That's what Lego is doing I think. Same could go with figures. I'm sure >75% of Infinity gamers consoles are connected to the internet or could be for a brief time (ie: Dad installs and disconnect).