Compose could watch your code and automatically kick off builds when something changes. This would mean:

• Code can be reloaded automatically regardless of language. This would also make code reloading work on compiled languages if that was part of the build process!
• Volumes are no longer needed in development
• Production server can be used in development (e.g. gunicorn can be used to serve Django apps in development)

It could either be an option to up (docker-compose up --watch), an option in the config file specifying directories to watch/ignore, or perhaps a separate command (docker-compose watch).

Thanks to @samalba for the suggestion!