It's been ten years, so it's gone beyond "idealistically".

It hasn't been anything close to that long since major libraries mostly worked on 3, though. You can't just declare the old version of a major software ecosystem dead because you updated one part of it. We've seen it with operating systems, we've seen it with browsers, and we also see it with programming languages and all the libraries and tools that make them useful.

Still not distributed by default on Mac or Ubuntu long term release, unlike 2.

The current Ubuntu long-term support release is Xenial, which comes with only Python 3 installed. If you're talking about Trusty, its support is ending fairly soon.

On Xenial, you have to separately install an optional package for Python 2. When you try to run /usr/bin/python on a fresh Xenial install, it'll tell you that you need to install a package such as python-minimal==2.7.11, whereas /usr/bin/python3 is already there.

Woops, my LTS is obviously out of date. Thanks.

It has not been ten years, as only Python 3.6 and later is considered finalised.