MythTV 0.20.0 is released. The upgrade went very smoothly for me. Here's the recommended procedure:
1) Stop mythbackend. 2) Dump your myth database. Just for safety. 3) Upgrade to new version. 4) Start mythbackend. 5) Start mythfrontend. You should see a notice scroll by about the database being updated.
That's it. Worked right out of the box.
Please file a bug report if your results vary. We want to make Arch the best Mythtv platform out there!
Plugins will follow shortly from Travis in [community]. Many thanks to him for continuing to keep after those.