In case (B), which seems the best according to t3a, if the miners are in charge of checking the behavior of the masternodes. What if there's a 51% attack ?
It isn't a good case because miners don't need to be running a masternode, they can just lie about facilitating coinjoins. There is no way for nodes to audit them, so what is the point of a miner not working on the lying tallest chain which happens to be valid?