I'd really need to think long and hard about it, but my initial feeling is that we'd attach them to data classes or a similar new construct. I don't think you'd want to reason about the blast radius with ordinary classes. Granted, that's more language complexity, creates two unequal systems, and makes much more to reason about. There's a lot to juggle.

As much fun as putting a PEP together might be, I don't think I have the bandwidth to do so. I would really like to see traits in Python, though.