I think that the mobility between the classes should be influenced by the player. I like the 4 tier system brought up, but I think dead nobles should be replaced by the player if the player wants the noble replaced. I think all nobles should have some sort of job with a related skill, so for instance the manager could have a manager skill that would effect the accuracy of assessments and how rapid/effective orders are, so say a dabbling manager might only tell you your entire created wealth is around 200000 and take forever to issue workshop orders, whereas a legendary manager would tell you your entire created wealth is exactly 239546, break it down into all the categories, give you a prediction of what your wealth will be and records of what it was beforehand, and get orders sent at a rate rivalling the modern internet. I think that the player should be able to basically pick anyone to be the new manager, and what the player goes by determines what the governments like, for instance, some players might pick any worker to replace a dead manager, some players might only pick double-legendaries or above. Normally, teir 4 nobles would just arrive, but if the player is strong enough, maybe the player could kill the king on purpose and replace the king with their favorite dwarf after defeating hordes of military. Essentially, the player could cause a revolution eventually :p Basically, I would suggest any system that gives the player more choices and more freedom.