I think for most use cases you can consider spawnfest/bakeware which packs a single executable which contains a launcher and an embedded archive.
I’ve indeed been toying with the idea of building an entirely independent Mac app bundle that is compatible with Sandboxing etc and around the existing Elixir releases concept. Since I don’t know how to write applications well for Linux / Windows I’ve focused on Macs. A particular concern that came up pretty quickly was handling of dynamically linked libraries, which I have had to manually relocate and then rewrite the entries in shared libraries within the release via a build script. So far the solution works for OpenSSL and I am sure will work with most libraries, but it has been quite an ugly experience so more thinking and studying is required to simplify it.
I have tried this approach with a Phoenix app and a Scenic app and more or less things work and I could put the app bundle on another machine and it works properly. (Usually Erlang is installed on top of OpenSSL installed via Homebrew on Macs so a simple Elixir release won’t work on other Macs without Homebrew / OpenSSL.)
For Windows, the same technique which was used to build portable apps could probably be used. I’ve not studied how though.