Buma/Stemra seems to be a mostly Dutch thingie, so it's natural people who aren't Dutch don't know about it. That considered, the question whether MaSu would join the organization is about as relevant as "Will MaSu go to the moon in the next five years?"
Ofc, MaSu will eventually go to the moon as it's a natural staging ground for universal conquest after global domination has been achieved, but that isn't likely to happen in just five years.