http://opengameart.org/content/faq#q-ccgplcompat
My question is.....can assets have different licenses when dealing with GPL? For instance, one tileset is GPL 2.0 and the other tileset is CC-BY-SA 3.0 . Can I keep the licenses for each one separate when dealing with GPL? How does this affect Solarus with distribution because Solarus and Solarus Quest Editor are under GPL v3.
About compatibility between your assets and the engine licence, the subject as been discussed here : http://forum.solarus-games.org/index.php/topic,101.0.html
About conflict between licence in the same part of the game (here, the quest), I don't know.
http://forum.solarus-games.org/index.php/topic,101.0.html
Ah, so they can have separate license from each other.
For the quests in the same part of the game....I think it is okay as long as I keep both tileset images separate. For instance, I won't be able to make a tileset with GPL 2.0 and CC-BY-SA 3.0 combined (mingle) on a single image. This might means that I probably won't being able to use both tilesets on the same map unless Solarus allows two different tilesets to be opened at the same time. Solarus would just be loading different parts of the image and won't actually be producing images that will be used. Kinda like an emulator.
That might be a good feature. A tab where you can choose a different tileset. RPG Maker Ace has a feature like that. With A,B,C, etc tabs. It might help with conflicts with different licenses.