The suggestion has been seen before, and I agree that it would be very nice to have.
It would also be nice if it stored the topics longer. My channel occasionally loses it topic for whatever reason (Undernet) and I have to go put it back in. Half of the time, the topic is in the recent topics dropdown menu and half of the time, it's not. I'm assuming it's based on how long since it was changed or added. I'm usually on 24/7, so I only ever see a topic when I join (rarely) or when someone adds or changes it (also, rarely). It would be helpful if it stored it "forever" as long as you don't leave the channel.
