Three new types of classes that have one thing in common: You don’t get them by promoting Hearthlings, they are accessible via immigration only, a passive class if you will. The chance of that happening occurs only after your village has reached a certain (biggish) size.
They also have one more thing in common: You don’t get to tell 'em what to do. Beggars are as unwilling to work as nobles and royals. Beggars eat food and function as some kind of food sink. The rich ones do, too, only they actually pay for services by ordering certain amounts of food or special kind of furniture. Before a noble moves to your village they order a mansion to be built, maybe a certain special template you only have access to under these circumstances or just a building with enough space.
By not being able to command the new classes they act as quasi-npcs that populate the village without straining the CPU too much by difficuly AI calculations thus allowing for larger towns than what we have now. After a certain number of nobles and royals have moved to your city even the king might consider moving his seat into your city. Before he does so, he might order a summer residence to be built. Whenever the king is in town, morale goes up, traders are more frequent while the likelyhood of attacks rises as well.