It is expected that as Bitcoin gained popularity, people would disperse to other internet places, because that's basically what happened with the older forums, people went to discuss Bitcoin on other social media, like Reddit, Youtube, Telegram, and so on, and if they are real fanatics they could even create their own things and gather their own follower and maybe even get monetized and earn real money with their contend.
That's the path that all internet followed and I doubt things would really change even if the alleged merit farming issue is solved.

Another alternative would be just ban people from posting in this thread if they are repeated offenders, how hard would be ban certain users from posting in certain threads?

Also be low rank is not a funny place to be if you want to post, because of the timeout between posts, so ranking is a factor that may cause a good poster be more or less engaged in the forum.