In addition to making reftest more consistent with our other harnesses, this will make it easier for us to schedule specific reftest manifests in our scheduling algorithms.
Adding some bugs that might be relevant to your interests.
I got decently far here and have some patches to upload. However thinking about it, this doesn't technically block my work in bug 1608836 and is ending up being a little more difficult than I anticipated (we'll need changes to how the build system handles test packaging as well as to the reftest mach command).
So there's a good chance I end up dropping this. Though I'll keep it assigned to myself for now and see how things shake out.