The merit requirement does prohibit most shitposters from ranking up, but it doesn't prevent them from participating in bounties. We've had this discussion before, and it's off-topic here, but I think if those bounties would require a minimum rank OR a minimum amount of earned merits, that'd be the final nail in the shitposting coffin.
According to hilariousetc on another topic, giving a merit requirement for joining bounties will only make them want to buy merits from other sources.
In my opinion, this can be both good and bad.
Good because we can identify the unscrupulous merit source and theymos can remove their privileges accordingly.
Bad because some people who made good posts but not yet received enough merit would have to wait - so I guess its a job better left to the hands of the bounty manager
Problem with these steps is that it will affect genuine users registering on the forum as well.
You refuted your own suggestion. 