Another idea:
~like the old quill stem idea, except inside a seatpost.
Why?
1.the clamping from inside and out would mean it is more secure.
2.the clamping on the inside, along with the bolt on the inside, would give the post another avenue and more material to dissipate vibrations.

diagram of how this would look internally:
~consider the fat internal part mobile/adjustable so that it can be clamped at the same altitude as the external seatpost clamp ~ in the same way that threadless stems clamping onto a carbon fork can have an wedge inside the fork to give the stem more solidarity.