This post will end up a mish mash of thoughts rather than a logical argument, but here goes.
Iran is a theocracy. That to me is the big issue. It's not like Iraq or Syria which were single party states with a bit of religion. Nor is it like former communist states, again single party, where the change was just political. It's not even like a religious state moving to be secular. Nope, it's a full on theocracy.
With that in mind, then without accurate data on how religious the population is, it's impossible to say how change can happen. Because we can't say for sure what change, if any, is wanted.
And yes, I have seen that survey that is going about. But that survey is flawed, as the survey itself says. Surveys in single party states/ theocracies are very difficult to do. Single party states because such surveys are illegal, and theocracies have the added issue that it will be a "sin".
I reckon the closest country Iran can be compared to is the Vatican.
That would be my starting point as a thought experiment. How to change the Vatican. Does the Vatican want to change, what does it want to change to, is their support for change ?
Will break this post here. Apologies to any Iranians reading this who are angry at my post. No offense intended. And TBH, the voices of ordinary Iranians are missing, for obvious reasons.