My post that you're responding to specifically said without being asked by their liege, so your argument is invalid. Using passive voice to say "it is suggested" when it's really just you suggesting it, with no connection as far as I know to Paradox, is hardly convincing. If Paradox didn't want this kind of feedback the mods would've done away with this thread. Also, I really don't care about how likely it is or you say it is that this gets implemented, I would like it so I'm suggesting it. This entire discussion is a waste of everyone's time. We should restrict the discussion to the pure merits or lack thereof of the ideas being discussed.
Right. There's a cost, and I trust Paradox to figure out what it should be if they want to add this stuff. I'm not even entirely sure whether the decision lets you convert to your liege's religion if it's in another religion group, it might be just within the group, like catholic to orthodox, but whatever it is that's already implemented I think could be good as a decision to convert to the primary title's traditional culture and religion. Maybe the cost for those would be higher, that's up to Paradox.