I think the reasonable middleground for most Python devs right now: if a medium or large project already written in Python 2 is working well, you can keep it as

I think the reasonable middleground for most Python devs right now: if a medium or large project already written in Python 2 is working well, you can keep it as is, but new projects should be written in Python 3. That unfortunately isn't an option for many people in corporate and other bureaucratic environments, but when it is an option there's no reason not to do so.