Since Docker is the one and only officially supported deployment method from 12.0, it should be made more flexible and more compliant with containerisation "best practices".
To that end I would propose that there needs to be a Docker image running only Seafile components inside (or perhaps separate images for seahub and the server), allowing users to mix and match them with external, manually configured webservers/reverse proxies.
The existing images that come pre-packaged with Nginx could be made to inherit from these smaller, Seafile-only images, so there will still be a simple "out of the box" deployment option.