i think jeans sitting can be very dangerous if done full weight for extended periods. i've done it many times, but only for 20 minutes to an hour or so, but i still just can't get myself to enjoy it at all. It's more like real sacrifice to me than pleasure, especially compared to facesitting in lingerie or nude, which seems so much easier and pleasurable.
Despite that, for the right person i'd become a 100% faceseat for her jeans. i can think of a couple of Goddesses i'd do that for.