Should I just relax on the proprietary seatpost thing? My logic is they supposedly have less issues with fit, and are more comfortable. If neither is a big deal then I will just get the Elves Falath Pro I really want.
What i would do is ask for a spare seatpost when buying the frame, that way you can sleep at night. I do that with rear mech hanger as default, same with spokes.
Most western bike brands make proprietary seat posts (it's probably a tad more aero, but i think it's mostly to charge more, essentially), so when these open moulds are made, i think it's fair to expect similar non standard posts.
Rule of thumb, it seems gravel frames have standard posts, road ones are D shaped, 1 way or the other.
Edit: The frame "Taiwan Made T1000 FASTERWAY Disc Brake Version O2 Carbon Road Bike Frame:Frame+Seatpost+Fork+Clamp+Headset,EMS Free Shipping" sold by "taiwan factory bike parts Store" on aliexpress seems to have a round seat tube, just came across it.