This is sort of an RFC task:
We provide only limited support for Python 2.6, and due to dependencies packages dropping support for Python 2.6 fairly regularly (See T72987: Python 2.6 issues (tracking)), it would be wise to state that the stable 2.0 release of Pywikibot can only support 2.7+.
Also the fix for T102461: Python issue 10254 hasnt been backported 2.0.
Also, Python 3.5 and 3.6 are likely to have some unexpected surprises. See T106224: Python 3.5/3.6 compatibility.
Currently the 2.0 setup.py includes only 2.7 and 3.3 ; we should add 3.4, and lock that down as the official support matrix for that release.
(... and get out a v2.1 or v3.0 which includes 3.5 in its support matrix)