Create a Knowledge Base of Game Companies' Streaming Policies
Videogame Streamers are already obligated to set their game as the category they are streaming. When a game is selected, have a link appear to show that game's company/producer's streaming policy.
The Streaming Policies would outline the rights a game company/publisher gives to streamers regarding streaming/monetizing their content, and whether they give (or can give) permission to use music from their games.
This would necessitate putting together a knowledge base of streaming policies from the thousands of game companies and publishers out there. A daunting task, but the threat of DMCA strikes are daunting for streamers, so a heavyweight in the industry like Twitch helping out by putting one together would be far more fruitful than some streamers haphazardly putting them together themselves.