nothing is blocking. it's just a good example to post on "why we dropped 2.6 support". Up until now travis is taking care of the 2.6 testing and I'm not seeing lots of tests failing solely on 2.6 (meaning, we're not used to write code that works on 2.7 and not on 2.6).
That being said there are a few places where we used a compatible syntax (or it's there since the beginning of times) that could be refactored to work on 2.7 only, but that's pretty much about it.
PY3 support, on the other end, is a total different story.