How exactly is this a compatible change? If cfeature contains keys already in feature, they are now getting deleted instead of keeping the value they have in feature. I would strongly recommend you get more careful with your proposed changes and actually fully think them through.
And with you now suggesting - also as a viable candidate I am going to direct you to: Dictionaries should have key-based set operations
There have been many such proposals, but most of the fizzle out, and I am not really sure why. But I wouldn’t focus on ^, - seems like a better candidate, for that there are quite a few usecases.