There’s a thread on this a while ago:
There was no follow-up, but from the linked musl mailing list response, it seems like most of the technical difficulties around detecting musl have been cleared, and the main obstacle is someone to champion the effort to research related distrobutions, and either propose a manylinux equivalent, or a way to incorporate them into the manylinux specification (if musl is found to have a common ABI to glibc where manylinux concerns).