Seeing that the mod embeds mixin without doing any relocation, it would be advisable to create another release that doesn't have Mixins embedded into it to allow compatibility with mods that already shade mixins / depend on a booter for mixins.

Mixin is by design not supposed to be relocated. And I don't see any scenario where providing a version without bundled Mixin would be much better than the version with it. The fact that legacy Forge is lacking proper dependency management doesn't change and you still need to manually ensure that the latest version is loaded first, whether that's by installing/renaming one file to be alphabetically before the other, or by replacing one version of RM with another one, doesn't seem to make much difference.