Reading "If you're starting a brand-new application today, there are plenty of valid reasons to write it in 2 instead of 3. There will be for a long time." on the same day it was written is not the same as 6 months or a few years down the lines.
I don't actually know when this was written except for the copyright: 2014-2015, so it can't be more than a bit short of 2 years ago.
It's one of the more irrational and idiotic suggestions I've ever come across. One of, if not _the_ most important piece of metadata for anything that has or will ever exist is its creation date. In particular for writing, putting it in a historical context usually makes the piece more powerful and increases your understanding of the subject. If it's bad writing then it's not going to have a chance anyway. Sorry to say but that may be true of the post in question. I was under the impression that due to poor Python 3 adoption, Python 2.7 would continue to be supported.
I second OP, please date your blog posts.
This has been true for the last seven years, and I certainly don't see it changing anytime soon.