Adding Python 2 support is a nice to have feature for the VFX industry. They are slowly moving towards Python 3 for their libraries (vfxplatform.com) but until then it's good to support compiling Krita with Python 2.
Python plug-ins now respond to the X-Python-2-Compatible option. Whenever they are not compatible, they won't be loaded by the Plugin Manager.
A couple of plugins have been converted to support both versions and are marked compatible for 2. This means it is compatible with 3 by default.
Tested on Linux (Fedora 26)