A current project at work can easily have many daemon processes with differing number of running instances that may need to be adjusted frequently. Deploying with Supervisor can be a problem given the amount of time Supervisor would take to start/stop processes.
Plug installs each package into a virtualenv then uses runit to manage each daemon instance.
I have a prototype version working now with a packaged version to come in the next few weeks after giving it more testing.
The biggest issue is after watching To Package or Not to Package I am falling in more of the "to package" crowd and despite Plug being a packaging solution smells a bit too much of NIH.