So what I'm working with now (subject to change):
You have 3 appointment slots that you start with: manager, broker, bookkeeper. You can appoint any worker to these positions, and your worker can keep their regular job. I haven't done the sheriff yet, but you can appoint one once you get 20 dwarves. You don't have to, but there should be downsides to that.
There is also an expedition leader. This isn't 'you', it's just the expedition leader. If the expedition leaders die, the dwarves will select another one, based on the candidates' skills and their friendships. Once you get further along, this leader becomes the mayor and will be elected more regularly. For any complaint meetings, there are some conversation skills that can augment the effects of the meeting.
Leader/Mayor: for now, just takes complaints from people, as it is now. The new venting complaint gives unhappy units another chance to get their mind at ease. As your fortress gets larger, you might want your leader to do less work so they can take more complaints. If the game can detect poor decisions later on (an easy one is a cave-in, for example), the leader would be somebody to blame. If each decision you make with the interface could ultimately be tied to an appointed dwarf or the leader, it would be fun to let the blame and accolades go around.
Manager: lets you do work orders and takes complaints based on availability of work and passes them on to the mayor (before guilds, which are gutted). Once your fortress gets large enough, a manager must validate work orders with a job in their office so that you'll want to free them up from other jobs. I haven't had a chance to test this out yet, so we'll see how annoying that is vs. sleep/eat and so on, but these appointed nobles should be doing things instead of doing nothing. There's an organizational skill that the manager has, though I'm still working out how that works with the manager screen.
Broker: gives you value information based on their skill at appraisal. Uses conversation skills at the depot to perform trades. Cannot trade without *somebody* at the depot, but it won't have to be your broker if you can't get them there. I'll have to handle how that works, but that's the idea. The broker also runs your shops before dwarves handle them, as it is now (bookkeeper no longer does it).
Bookkeeper: the bookkeeper handles the stocks screen. If you want precision when the numbers get larger, you'll need to let them do an office/stockpile wandering job that works with their record keeping skill.
These dwarves will also meet with the various critter diplomats that come in as they do now, but I haven't done that yet.
The various guilds and other extraneous nobles are now temporarily gone. We'll see what I get to, but it'll all come back in over time. The guild leaders should be selected by the guild members from within. A few things like the dungeon master and alchemist are still floating around and kind of the same. Things like the house of death and the weapon cults won't be back until I get shells of religions in.
The baron/tax collector/hammerer are still external. The idea is to have the baron turn into a count then a duke as your fortress improves. I'd consider doing various other things with this (like having the king turn one of your dwarves into a baron instead of bringing in his cousin or whatever), but not yet.
Hopefully, the end result after a lot of tweaking will be fewer nobles, and the annoying nobility aspects of the appointments are mostly gone. Things like "treasurer" and so on are just going to be name changes based on the size of your fortress. Depending on how much the appointed dwarves are tasked, there might need to be additional subordinates or something in a 100+ dwarf fort, but that'll depend on play-testing.