Thinking a bit further, there is definitely a decorator-like pattern underlying the Ammonite/Mill/Cask implementations of entrypoint functions that could conceivably become a language feature. However, extracting that out, defining it, and making sure it’s extensible in all the right ways, is a deep discussion in its own right and probably out of scope for a discussion based around simplifying main methods and getting started for newbies.
Proposal: Simplifying the Scala getting started experience lays out what I think we should do to help beginners. I don’t think it makes sense to discuss @main method language additions and specs in the abstract without the proper context of how it fits into a larger strategy.