right now, If your goal is to create a game marketplace where games all look the same, these licenses are on the right track. The Pro license allows modifications to assets but then says the 1 allowed derivative is owned by the seller, which doesn't make any sense. The license just needs to say any derivatives have the same restrictions as the original; I don't know what incentive a potential buyer has to modify any asset if the seller can just take those modifications and re-license the entire derivative work to anyone else at any time. Buyers have limited ability to differentiate in their games based on these sorts of terms.