I've been experimenting with using NetBSD pkgsrc on musl to see how far it goes. Many hundreds of packages compile and pass all their tests, including, for instance, every major language interpreter, various development libraries and resources, and XFCE4. Things that don't compile usually fall into one of two categories: (1) using #ifdef __linux__ to mean #ifdef __GLIBC__, and (2) fundamentally unportable packages that have huge hacks for every single platform they support. There's rumbling about creating a package support wiki where people can document what packages work, don't work, or require patches to work, but it doesn't yet exist.