I finished my migration of a first Plone addon some a week ago sucessfully and started with migration of a further addon, collective.dexteritytextindexer to Python 3 compatibility. I was able to migrate the source code of the addon itself, but run into issues with the behaviors test script. The tests ran successful on Plone 4.3 to 5.2 and Python 2.7, but failed on Plone 5.2 on Python 3.