The open rebellions are a neat idea, but I feel like they're implemented a little badly. It seems to me that they're intended to make culture more important, and punish you for not keeping your culture up besides the extremely slow, easy to counter enemy culture creep, which is a good idea on paper, but the way it works in-game I think is not so great.
For one, it's infuriating to have a single planet constantly suffer from open rebellions over and over, I think a planet ought to be unable to have an open rebellion for like 5 or 10 minutes after colonization. It's very silly to me that I can colonize a planet and then almost immediately have an open rebellion before I even have enough time to set up culture.
I also think that the check for allegiance should somehow be applied before planet bonuses such as ordered society, death world, etc. My reasoning for this is that I find it very annoying that I am being punished for something I have no control over, it might not be feasible or even possible for me to get my allegiance past the maximum just because of planet bonuses.
Basically, what I mean is, let's say we have a Death World, it gives, among other things, -15% allegiance, it's far from the capital, so it has the minimum base allegiance of 35%, reduced by 15% by the death world thing, to 20%. I think that the open rebellion check ought to see the 35%, rather than the 20% after the bonus, since we have no control over what planet bonuses we get. I dunno if this is feasible, but I think it would make open rebellions a lot less infuriating!
Edit: Reading the OP, I see it's only supposed to happen if the planet is affected by enemy culture, but this is most DEFINITELY not the case. If it were this way, I think Open Rebellions would be totally fine even without any 5-10 minute immunity after colonization.