Is there a non-proprietary standard for oval seat-tube/post? I see Pinarello Dogma and Gan S frames have a proprietary seatpost/seattube combination, which don't have a circular section. An advantage of that design in my opinion is that it's impossible to have the saddle not aligned when adjusting the height of the seatpost. One disadvantage I can see is that if the seatpost is not properly greased and get stuck, you don't have much freedom of movement to leverage on in order to unstuck it. In any case, I was wondering:


  Is there any standard for seatposts that don't have a circular section?


Say one wants to build their own frame with this feature. Is it possible to have this on a steel frame? And if it exists, what's the most common standard so that it's easy to find seat tubes and replacement seatpost?
There has been in the past--Shimano once had aero group variants (Dura Ace AX and 600 AX), which included an aero-section seatpost. I had a bike that came with one such seatpost. Unfortunately the binder clamp on the seat tube didn't quite keep the seatpost in place, and I had to have a framebuilder tap a hole for a setscrew.