I also think there are 2 other big downsides to the ‘bringing back threads to the top’ approach:
1. Loudest mouth gets to dominate. The loudest people just get to keep bringing their threads back up to the top, even if the topic of discussion isn’t of interest to most people, because they can just keep replying to each others’ posts if there are 2 of them.
2. Important posts that don’t generate replies - like the Co-op newsletter - get lost much more quickly. This means the function of this board as news source is lost.