I don't think you should be afraid of removing backwards compatibility. Look at WordPress that has maintained backwards compatibility for too long. It will happ

I don't think you should be afraid of removing backwards compatibility. Look at WordPress that has maintained backwards compatibility for too long. It will happily run plugins that were abandoned ten years ago. When you break compatibility, you force out abandoned crap. I agree you don't want to do it too often; but not doing it at all is (IMHO) worse.