Indeed it will break every existing non-trivial Python program.
I hope someone big and important like Ubuntu or Red Hat does a fork for compatibility (they could call the fork "Real Python", and start version numbers at 4.0). Oh well, at least it gives me an incentive to learn Ruby.
2.6 is for backwards compat, with as many of the 3.0 features as they could do without breaking changes. And frankly other then the whole GIL thing Python has been moving in a pretty solid direction all these years, so eh.
I attended a Python3000 talk by Anthony Baxter last month (Anthony is the release manager for Python).
He mentioned that Python 2.x is will be supported for a very long time. They definitely expect to have 2.7 and may be even 2.8. They are also going to backport important features and security fixes from 3.x
Google has a very large codebase written in Python 2.x, it's in their interest to support the language for as long as needed.
I hope someone big and important like Ubuntu or Red Hat does a fork for compatibility (they could call the fork "Real Python", and start version numbers at 4.0). Oh well, at least it gives me an incentive to learn Ruby.