Our Roll20 integrated audio feature is not yet on the live server, only on dev. I don't have timelines nailed down enough to discuss things much beyond that, but once those integrations do come to the live server, selling audio on the marketplace is something we greatly desire. However, once we do incorporate such, it will follow the same rules as everything else on the marketplace - we generally don't allow free content, and push very actively to ensure people who make great art get paid for such :)
