I think something like this would be a good idea. As it is, the level of micromanagement required to run the fortress decreases pretty smoothly as your population expands, as it should. It's like zooming out from The Sims level to maybe Pharaoh or Caesar level. But it doesn't go far enough.
One of the things that does really bug me mid/late game is labour assignments. We shouldn't have to download third party programs just to manage who does what in the fortress. It gets tedious when you have around 80+ people, especially if their primary skill (their icon) is different from what you have them assigned to.
So I suggest a similar process to the noticeboard: once you get a guild, jobs from that profession become privatised. You designate them to be done, and then the guild (if they have a guild office designated or something) employs someone to do them for you, probably someone with high skill.
Maybe this ties in with the dwarven economy when it returns; instead of being assigned labours, everyone becomes available for employment in any field. When there are lots of one profession's jobs to do, lots of dwarfs have opportunity for employment in that field. Maybe you don't have enough skilled workers to fill them all, so base salaries increase with demand. If you have hardly any jobs queued up from a profession, then all but the highest skilled get laid off and have to look elsewhere, maybe becoming haulers, maybe getting jobs filling in vacancies in a trade with lots of job openings (but getting paid less because they'd be Dabbling).
Maybe each guild should charge interested dwarfs a bit of cash in return for some basic training in that trade.
Then your large fortress always has exactly as many workers in each trade as required, without you having to micromanage each dwarf's labours. Provided you have the population to supply all the work, of course. The manager should give you an idea of the unemployment rate too.
Obviously the player should get to dictate a minimum skill level for guilds to hire, again through the manager. And just to give completeness, the option to manually change labours on a dwarf has to stay in as well.
I think something like this would make managing larger fortresses much more bearable and fun. Time freed up to focus on ruling, not on frankly tedious labour micromanagement.
Edit: added breaks to remove BIG WALL OF TEXT