On the call yesterday, the topic of dropping support for Py2 came up.  This site provides some context:

At present, we're planning to have a 3.4 release sometime in the early summer, and then aiming for a yt 4.0 sometime about six months later.  yt 4.0 will have the demeshening.

A proposal was floated to have yt 4.0 be the last release that explicitly supports python 2, and then to "softly" drop support for python 2 during the cycle for yt 4.1, which would be about six months later, we anticipate.  This would mean not testing on py2 anymore and potentially removing some of the shims and six calls to dual-support.

Some more discussion is in the meeting notes:

I don't know if this is something we should actively discuss yet, but I wanted to put it out there.  I personally support this proposal.

-Matt