Who knows why Tesla pulled them, don't think they ever said, just speculation on people's part. My theory was based on first of all they were offered in the MX solely, being a more expensive car than the MS. I'm sure Tesla ordered material in bulk for their vented seats and when their inventory to cover seats was starting to run low and it was end-of-year push for sales on the MS, decided to offer it on the MS as a "luxury PUP bump" to help use it up. I feel very fortunate to have gotten it on our car.
BTW when you have thinner clothing material on you definitely can tell the difference on your back especially when you have the venting turned up to 3. We don't run with it on all the time, but when the temps are in the 90s+ definitely will turn it on as soon as our backs start to feel too warm in the seat.
As for covers on the seats. Tesla warns against using them if not mistaken. Has to do with sensors and air bags as I recall.
We have some wrinkling in the front seats that we sit in all the time and honestly not an issue like it seems to be for some here. Haven't seen any signs of wear. We do try to practice lifting ourselves out of the seat as we get out instead of sliding over and leaning out.
As for M3 with or without vented seats, I would hope as production would start to kind of level out to meet orders they would include the vented seats as an option at least on a PUP package. I know right now they want the least amount of variation in orders to be as expeditious as they can be in getting cars to customers.