Larry Hastings: "Victor, what do you think, does this need a 3.5 backport? I'm inclined to say yes."
Naoki has to design an evil object which triggers explicitly the garbage collector to get a crash. He found the bug by reading the code. I don't remind anyone complaining about the bug. So I don't think that it's a major bug, as was bpo-21435 which was *easy* to trigger using asyncio.
So no, I don't think that this issue desevers a backport.
But it's just my opinion, feel free to backport to 3.5 if you consider that the bug is critical enough ;-)