Thanks for the post, but I hope you reconsider using Cuben Fiber. I really like the front entry design of the Contrail and Squall 2. I bought a Refuge X. It is indeed an excellent tarptent. However, I can't get my wife into it and I'm considering selling it (as I'm not that comfortable being in it, either). This has nothing to do with the material, but everything to do with the design. This is a personal preference, but one shared by my wife and me: we both prefer the peak of the tent to be by our head. I like as much room by my head as possible. Again, there are probably plenty of people out there who feel otherwise, but we both feel the same way. So, in that sense, I have to respectfully disagree with your statement about their being "plenty of Cuben Fiber shelters out there". My apologies if I am missing something, but I don't believe there is anything similar to either a Contrail or Squall 2 in Cuben.
We own a Squall 2 and I would buy a Cuben Fiber version if it would save us substantial weight. Are you sure it would only save 4 ounces? The (silnylon) Refuge is 27 ounces, while the Refuge X is 16 oz. I believe the floor is the same. Perhaps you've done the math already, or maybe you are considering a heavier weight version of Cuban Fiber, but I would be surprised if you only save 4 ounces if you made a Squall 2 in Cuban.
If you prefer to not work with Cuben, that is understandable. I hope you don't base that decision on your assumption of the ultralight crowd, though. There is a big mix here, but there are plenty of people here who will pay top dollar to save a bit of weight. Many of these folks aren't rich, they just spend their money on gear (as opposed to other things, like big screen televisions). If you aren't sure if folks are interested, then I suggest taking a poll. Again, this is up to you -- it's your company and you can do what you want. I'm sure designing new tents is probably a lot more fun than working with a new material (especially if that material is difficult to work with). But if you run the numbers and do a poll, I bet you would find that there are lots of people interested in paying a bunch of money (hundreds, I wouldn't say thousands) to save a little weight. Ron Bell has been successful knowing that we have that attitude.
One of the first things I learned about ultralight, is that you have to make trade-offs. I personally take the attitude (and I know there are plenty like me) that if the only trade-off is cost, then I pay the money.