A post on the Edit Blog (a leaky FCP 6 graphic?) reminded me that I wanted background rendering in Premiere. Avid Liquid has been doing this for a year already.
Happily things are better in After Effects. Nucleo Pro enhances AE quite a bit, and I wish Premiere could use it too. Anyway, you can still do background rendering to a file in AE without Nucleo Pro, as explained by Jonas Hummelstrand and Lloyd Alvarez last year. See how to manually set up renders in AE in the background for Mac or Win in Jonas Hummelstrand's General Specialist article.
Last December, Lloyd Alvarez released a script on AE Enhancers called BG Renderer that "takes whatever items are queued and ready to render in the render queue and sends them to render in the background using aerender in a new Terminal (mac) or Command (pc) window where the render progress can be monitored. It also had the added advanced feature to launch more than 1 instance at a time."