Is there a non-proprietary standard for oval seat-tube/post?
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.