Hi @nils.schnabel,
I have actually been on 2.5.x until a week or so ago, since I had the this PR merged as it broke my scripts. Saying this, the 3.x version of the add-on that is present on the main ES6 PR worked fine for me once I updated.
As for merging the add-on to OH itself, I don’t have the ability to do that as I’m not a maintainer so don’t have access. I’m not aware of any blockers though so haven’t made any changes to it (although I plan to bump the GraalJS version soon to get private class fields). Saying this, I’ll mention Kai on the PR to see if I can get his attention…