34,9 mm is not a dropper post related standard. I had a Scott Scale back in my xc racing days in 2005 that had a 34,9 mm seatpost. As for binding and bushing overlap and the like, there are very few dropper posts that have a 34,9 mm specific upper (Bikeyoke Max series) as opposed to just running a thicker lower/outer tube with the rest of the parts the same as with 30,9 and 31,6 mm posts.