The discourse team didn’t contact me (perhaps this feature would increase the complexity of the project, but I think very little), so for now there is nothing (but the above should work anyway, although it wouldn’t be in the official discourse_docker repository).
@justin Actually my main reason isn’t even to minimize downtime, but keep a base image with all the ruby gems, plugins and the discourse repository already installed, which could be used in different environments, like staging and production, and even for different projects, if they use the same plugins, running only the db migration and assets precompile tasks (which must be run in the target machine), and would avoid problems when upgrading discourse.
The reduced downtime would be more like a colateral, a welcomed one. That said, in the end it’s up to the discourse team if this feature should be included or not, but I would be very pleased.