More developers who could submit patches instead of just report issues would help
(though just reports are also welcome), and more people implementing Musepack support in various formats, software and devices would definitely help it. As a user, you're already doing everything you can. Just using and spreading the word about it eventually results in more support, and that's a fact. Thanks to that, while more widespread support is desired, Musepack is doing pretty well right now. The ultimate goal is high sound quality for end users, and we're achieving it thanks to a highly versatile, implementable and optimal format for the purpose, great developers and great end users.