We really didn't intend for the RSL to run more than a 25c tire from the start. There is also just a bit more involved than making the stay longer. It has to do with the shape of the stay behind the bb where the tire will run. We have very specific tooling to make those "shapes" on the stays.
We do understand the trend of running a bigger tires and do so ourselves on many of our personal bikes. It's something we will look to address in the near future on the RSL, but for now, we are pretty happy where it is at. Going bigger than a 28c most likely won't be in the cards....when you get to 30c tires, you are looking at a long reach road caliper....for that we have the Vamoots LT. It would be possible to order say the Vamoots CR custom with PF30, 44mm head tube and be able to accomodate a 28c tire...still, normal road caliper specs.
Let us know if you have more questions....