No, it hasn't, based on download stats of packages. Guido found this out the hard way when he went to work for Dropbox. They run mostly Python 2.7 code, and now he has to maintain it.
Also, PyPy is 2.7 compatible, although there's a 3.x beta.
Also, PyPy is 2.7 compatible, although there's a 3.x beta.
That doesn't make Python 3 a failure or unadopted, it's just the structure of our industry. By search & job stats [1], the most popular programming languages are Java, C, C++, C#, and yep, Python. Companies tend to pick whatever language is best for early adopters when they first get started and then language usage grows along with the company. So the most popular languages now are the ones that were cutting edge 15 years ago, when the biggest companies of today were tiny startups. Go look at what's most popular among startups today and you'll see what'll be the hot programming languages in 15 years.
[1] http://www.tiobe.com/index.php/content/paperinfo/tpci/index....
I've done this anecdotally (i.e. not with a huge quantitative sample size, but looking at specific "hot" tech companies and the tech stacks they end up using) and it seems to work, but is subject to certain gotchas. Data points:
EBay (1995) - Perl, rewritten in C++ in 1997, rewritten in Java in 2002. Google (1998) - C++. Del.icio.us (2003) - Perl. GMail (2002) - Perl, rewritten in Java circa 2002. LiveJournal (2002) - Perl. Flickr (2004) - PHP. Facebook (2004) - PHP. YouTube (2005) - Python. Reddit (2005) - Lisp, rewritten in Python in 2006. AirBnB (2006) - Ruby on Rails. GitHub (2007) - Ruby on Rails. Dropbox (2007) - Python. Hacker News (2007) - Arc, YC internal tools (c. 2012) are written in Ruby on Rails. Twitter (2007) - Ruby on Rails, rewritten 2010 in Java/Scala. Uber (2010) - Node.js, supposedly this was a rewrite.
There are two big caveats:
Sometimes a big competitor comes along right when a language is undergoing a massive rewrite - for example, it looked like Perl would own the Internet around 2003, but just a couple years later we got Rails and Django and Perl stagnated with Perl 6, and so Perl jobs are nowhere near as hot as they would otherwise be. Similarly, Python was poised to take over much of the non-web server space in 2008, but in 2009 Node.js came out just as Python was losing steam in the Python 3 transition. Python still remains pretty hot (it's been helped by its use in data science), but it may've lost the startup server market to Node.
The other big anomaly is that there was a lot of attention around Haskell and Erlang from 2005 - 2008, and yet these are still niche languages. Erlang had one big success with Whatsapp and some smaller ones with Facebook chat and CouchDB, but didn't really become mainstream. My hypothesis there is that because both of these were old languages that were rediscovered, they were built with some assumptions (eg. strings are lists, or funky POSIX interfaces) that didn't fit modern startup development, and so they couldn't gain critical mass. But then, both Python and Ruby were old languages that were rediscovered; perhaps it was the sudden resurgence of Linux (which both Python and Ruby were steeped in) along with the web that carried them forwards.
New companies, like the one I'm part of, use Python 3, all the time. Django, and the other 15 packages we require, all support Python 3. In fact, I've been using Python 3 since 2008, and I've been using it for work since 2013. I think we're past all of that, at this point.
I'm not sure why migration is always regarded as a metric for succes. Python 3 wasn't supposed to be a "upgrade", per se. It was supposed to allow the core to rid itself of a lot of the language's warts. It has done this quite well without sacrificing much. The result was a slow migration, not by existing code bases, but by means of new companies.