That's an interesting fact. I've just measured my seat pin, and it yo-yos from 34.05 to 33.79mm, depending on where it is measured. I hope it isn't wear.

As a complete aside, I've just folded my bike thus: front wheel rotates ~170deg to the left hand side, then seatpin is raised and rear wheel rotates under the bike. Front wheel passes between rear wheel and kick stand, so it can't rotate. Seatpin goes down and is clamped. The whole unit is then becomes quite a stable package and can be lifted by one hand and shaken around without the front wheel swinging.
For those having custom frames made in the future, a 1" spigot welded somewhere would enable the handlepost to be stowed securely, too, using its own clamp. Underneath and to the front of the top tube might be one place, but you might think of other places that would be better.