Sorry for being late in the discussion here.
In R20 python_init.py is no longer executed at startup of Cinema. Sorry this change was not documented.
The __init__.py script in the preferences path python27/maxon_generated was not meant for this but it can be used as replacement.
However, as Adam pointed out the difference in his last post here, the __init__.py script in R20 is executed after the plugins are registered. Pre-R20 python_init.py was executed before the plugins registration.
This means a plugin cannot rely on operations done in python27/maxon_generated/__init__.py.
Note the other Python files in the directory python27/maxon_generated (_configuration.py and _enums.py) must not be modified.