Once CK+ is able to jump to the newest (stable) patch are you planning on adding a few Hellenic rulers/country since it had some (very limited) influence during the new time period historically.
But not any majority in any province. Also, for gameplay reasons it would be bad to include them. CK2+ can't bughunt the last hundreds of a since long weak agonising dying faith. What is currently serves it purpose and is enough. For these kind of stuff, wikipedia isn't really a good source either and that article has a good name "decline of greaco-roman etc..." .804 Hellenes of Laconia, Greece, resist the attempt of Tarasius, Patriarch of Constantinople, to convert them to Christianity.[105]
source http://en.wikipedia.org/wiki/Decline_of_Greco-Roman_polytheism
That might be an idea worth thinking about at the very least, although then it should apply to all religions.