I have proposed and written an implementation that would modify the Dockerfile to build from the source code it's distributed with, as opposed to the current behavior of having a hardcoded release number which is fetched as a tarball and then built. Along with this comes a few other changes, discussed below.
This proposal is made at https://github.com/Cray/chapel-private/issues/3818. To summarize for those who can't access the private issue, this would allow building a Docker image from any version of Chapel, instead of just release versions. In turn that would enable a development workflow using Docker to build and execute Chapel, as well as opening the way for CI tasks to be done with the Docker image (which I may pursue in the future).
The implementation is in Modify Dockerfile to use source it's distributed with by riftEmber · Pull Request #20705 · chapel-lang/chapel · GitHub. This also includes several changes associated with the new ways the Dockerfile could be used, which are listed comprehensively in the PR description.
Feel free to share any concerns or comments on this proposal, either in this thread or (for specific requests) on the PR. Thanks!