There is a very clear cost for many new projects: infinite... for the simple reason that some key libraries still do not do Python 3 at all. Let's be clear. Cassandra is the best large ingest nosql database out there. Python 2 only on CQLSH. Bloomberg. The default terminal used by the 300 000 most important financial people on earth. API Python 2 only. Theano. 3.x via 2to3 only. Anaconda, 2 still the default download with 3 an afterthought (in other words, even for new downloads, 2 still the majority!). This is more than about stuff not being ported yet. It's about people preferring 2.x.

This idea that Python 3 is cost free needs to be expunged. For large classes of users, Python 3 is not possible even if they want to (which they don't). Stop this erroneous propaganda. Unicode is nice if you're a web guy, and if you're a web guy, why are you using Python already? Unicode is completely irrelevant for everybody else and is most definitely not a core reason to move to Python 3. You're living in cloud cuckoo land on your 3.x magic mushroom trip.

Earth to web jockeys. Python's hardcore is numerical computing, and that hardcore is not on Python 3, and is not moving anytime soon, and certainly not for the dubious benefit of unicode. Moreover the web stack is much less important to Python than is numerical and scientific computing, for the simple reason that while the former has multiple better competitors in the form of golang, JS et al, the latter does not.

[sidebar: since when does ascii not cater for accents?? I am bilingual french / english and I have never had a problem typing french accents in ascii? You're creating misleading propaganda again. Once again, EatHeart, I quote you: "I suspect you don't really know what you are talking about...", or worse, you have an agenda to mislead.]