Well, Swen recently wrote this...
"We're hoping Divinity:Original Sin is going to be a big success and if it is, we'll add *a lot* of extras. My hope is that we can make this a live game that is continuously improved and expanded upon, with plenty of mods appearing, and we're setting ourselves up for that. Of course we'll only know if this is feasible after it releases, because the sales will determine how much resources we can put into this."
I bet they've got more than a few ideas for potential expansions and such, though it's best if we don't know what they are in case the game isn't commercially successful enough to justify them. At least I don't want to know to avoid disappointment.
Larian have previously stated that they're not a fan of DLC (the typical nickel-and-diming model) so I would expect more substantial content than say horse cow armour which could just be modded in anyway.