Version 3.1.0 has been released a couple of days ago [1]. Would be nice to get it into the tree. Simply renaming the ebuild worked for me™. [1] https://www.mail-archive.com/announce@lists.open-mpi.org//msg00109.html
This is kinda blocked by #652432. I'd like to get pmix to support multilib and then use the system version in this package. I was waiting on hearing from jlec and got the go-ahead from him late last week.
Done, #652432 is a lot more work than I expected.