APC's very careful distribution strategy (a lot more cachet, and yet cheaper than even the lowliest pair of Sevens.
I think part of the reason APC is able to keep its price "low" is that it had moved its production base to developing countries. Most Nudies and True Religions are made in Italy and USA respectively, and I guess their price partly reflect the higher labour cost. As to whether a particular label will become mass market brand, it will depend greatly on who is in control of the financial matter. I am sure that Evisus and Nudie will not be content in staying as a niche market brand.
Jeans don't actually cost that much to make. I like premium denim, I buy and wear them, but let's be real. They cost a bundle because people (like some of us) are willing to pay a bundle. Denim is relatively cheap, even top quality selvedge denim, manufacturing is inexpensive here, in HongKong, or in Vietnam (although of course, it is relatively cheaper in Vietnam), and even the most expensive laundry treatments only cost something like $14 a unit, and that is one hell of a treatment, probably an intricate one with a lot of screwups. Evisu hasn't hasn't been a niche brand for a good part of a decade now, and Nudie could either go the way of Evisu (i.e. be pretty mainstream but still maintain cachet because the design is not geared towards the average customer) or of Paper Denim. I tend towards the latter because the cuts and details are much more consumer accessible than APC or Evisu, and because they have a large repetoire of laundered jeans (The raw jeans are what we talk about, but there are actually more styles which are laundered. I doubt that they will go the way of Seven, but Paper Denim, easily... Nothing wrong with that (Paper Denims are some of my favorite jeans, at least their old cuts and washes), but the cachet will not be there the way it is now.