This makes me uncomfortable. I don't exactly know why, but the thought that ideas, nice-to-haves, and bugs move to a /dev/null of some sort, does not resonate with me.
What if that bug re-appears after 7 months. You'd want to pull up the old one and go: "see, it still hardly ever happens, but here's another one".
You could rename the backlog to "archive", but that hardly makes it different: a backlog is still a list of stuff you had no time to think about.