This has the added benefit of warming up the app before traffic ever hits it, something I was always surprised that even heroku didn't do (at least, the last time I used it ~6 years ago)
I see compose in production all the time - especially from folks that want compose support _in_ Dokku. I bought this up with the compose project manager a few months back. It seems like an interesting use case but it didn't seem like the Docker folks were... aware that this was how folks used docker compose? There is a project out there - Wowu/docker-rollout - that sort of provides this but it has some rough edges.
My understanding is that they are focused on the local development loop at the moment, especially with the acquisition of Tilt. That said, I don't work there so take this all with a grain of salt.
No. With Dokku you can just push to git remote and it'll build, deploy the image, set up LE certificates, roll out the app with zero downtime (if you want). To get this running you'd have to do some manual stuff with git commit hooks, but that's just one small part of Dokku.
