After reading through this whole thread I am reminded why I no longer frequent the forums; page after page with a lot of fluff and off topic.
Coatings have their place but I think they are over-sold. Too often the customers take it as a license to neglect the vehicle, thus the benefits are often mitigated. If the goal of a vehicle is to have optimal appearance then regular detailing with regular proper washing should be sufficient. A vehicle that is neglected and might be given a little extra attention once a year, at most, is probably not going to benefit from a coating as any washes are probably going to be improper as well. A daily driver that is wanted to be kept in the best possible condition and the effort will be put in to do so is a good candidate for a coating.
What you choose to use on your own car is one thing. For a fair analysis we must view it from a customer's perspective. Most detail customers do not always follow our recommendations for proper care. Even with a coating it can be expected that they will cause swirls, scratches and marring through washing, drying, and general carelessness. How many are going to be disappointed after 12 months?
When it comes to sealants, when the durability is x-y months and the customer waits until z months to return, does it really matter how long the durability of the sealant was? The car has been unprotected and likely needs additional work. The same is true for coatings. Tell them it will last UP TO 2 years and they will wait 3 years and wonder why their car doesn't look the way they want. Since the interior of the car will need periodic detailing anyway it shouldn't be a problem to do periodic polishing and apply a sealant.
I think many detailers push coatings due to the reality that many customers are "one and done" types. Many customers tell themselves they will maintain their car but we all know that that doesn't usually happen. Thus, the detailers want to maximize the sale. It really isn't different from so many other industries. When I managed a snowboard shop the owner got upset that I missed an opportunity for a sale when a woman came in looking for a particular brand we didn't carry. After explaining the pros and cons of the line and why we didn't carry it she said it was a gift and that the recipient requested it so I referred her to another shop that had what she was looking for. About 6 weeks later the woman returned and purchased 4 full packages for her family, about $600-$800 each, stating my honesty and the information I provided previously as her reason to trust that she was getting quality, appropriate equipment and not just what she could be sold. Moral: you can shear a sheep many times but only skin it once. If we, as detailers, are less than impressed with the performance of the coatings, just imagine what the customers are thinking. How long before we are viewed the same way the stealerships are for selling their snake oils?
The way some (not all) of the brands have played games with price increases, exclusivity, contracts/requirements and insufficient support has been more of a turnoff as well.