The top post can be a wiki, and people can add updates/suggestions via reply, but the downside of this is that a) someone will have to edit the wiki to keep it inline with replies, b) the topic will only be bumped when someone replies, and not when the wiki is updated and c) members will enter the topic at the last read reply, as opposed to the wiki post.
Having two topics would work if one was a wiki (editable but closed) and the other was a discussion that people can reply to. This would be a good solution to preserve the existing discussion posts, but in future, IMO, we should encourage people to edit and improve the wiki as opposed to making replies that someone else then has to compile into the wiki.
Happy for my posts in this chat to be moved / deleted to avoid derailing your original topic.