This is great news! I would love to try your version of the plugin in a zip.
When you have different files with a main, which one is selected is arbitrary. It would be great to be able to choose which main file you want to use.
Also, when you refer to directories of of the scope of the IntelliJ project, the Elm plugin treats them as missing, even though everything compiles fine. IntelliJ is able to deal with files outside the project, so it might not be such a big deal to implement this.
Thanks!