I can chime in;
I started Pax Runner because back in the day, because it was really hard to write a bundle that worked on all available frameworks, and it was even harder to automate it. Alin Dreghiciu took over at some point and made Pax Runner into what it still is. That was in 2007 or so...
When Alin, I and Toni Menzel were on a project together, Toni and Alin proceeded to create/expand Pax Exam, a testing framework that leveraged Pax Runner to run your tests against all of the frameworks. In parallel a "native" test launcher was made in Pax Exam and at some point the Pax Runner launcher was dropped, and Pax Runner basically ended up being unmaintained from then on, mostly because it wasn't too hard to do the same thing with Pax Exam. I even used Pax Exam in 2011 as launcher on a project where we couldn't decide which framework to use.
So, most things that Pax Runner can do, can be done in Pax Exam (at least ver 2.x). But there is nothing stopping you from reviving it and take over maintenance. If one prefers config files over code, then that could make sense.
HTH
Niclas