Let’s say you have a topic start to take off, and it becomes clear a poll would be a nice addition to the conversation.
Start a new topic, referencing the original one which spurred the poll? Benefits here would be having the poll as the topic, so it wouldn’t be buried in the middle of replies, you could also name the topic “Poll:…” so people know it’s a poll. Cons would be even if there’s a link to the original conversation, you’re losing continuity and creating a branch from the original topic.
Simply reply to the topic as you normally would and insert a poll? Benefits would be cohesion, but it would be mushed in the middle of replies. I guess you could always rename the topic if you went this route to indicate there was now a poll.
Append the poll to the original topic (instead of issuing as a reply), rename the topic to indicate there’s now a poll, and reply to bump for visibility.