Came across this rhythm game site online instead of downloading songs it avoids it all together by streaming the videos from youtube. http://wimylime.appspot.com/list.htm got me thinking that if something similar was possible using some type of overlay on top of streaming Youtube videos it could really broaden song selections although online play would be required. perhaps eventually a web browser add on for Firefox which would increase userbase, Users could create gameplay files based on youtube video url, allowing you to choose from a list while selecting youtube song. Also could help with avoiding any potential copyright issues as there is only gameplay being distributed not the media itself.
Maybe Brave would also get one if this is implemented. I have no coding experience right now, though.
Although this is a cool concept, it’s not possible to do something like that without a complete rewrite of the StepMania engine.