One good way of marking dwarves for guilds is also sticking them in squads of the same name and requiring them to "sleep in a barracks at need". If all other guild-members are required to go to their "guildhalls" and just train there during a Player's turn, then they're effectively taken out of play for any of the other professions.
Players could bargain with other Players here on the forum for a guild member's skill - trading for an agreed upon item or use of guild members themselves in return, whereupon that guild member would be temporarily taken out of "training" mode by removing them from the squad and they can do their thing before being put back into "training" mode again by being placed back in the squad.
We'd need some dedicated farmers/brewers to take care of everyone's food needs, or we could make that the responsibility of each Player to support everyone on their turn and have the Player get an "forum trade point" for having extra food/drink stored at the end of their turn, but either way that should keep all the guilds-dwarves in their squads from going berzerk due to starvation bad thoughts.
If we do it this way, everyone could start out with 1 "forum trade point". 1 "point" buys a dwarf for your guild - On a Player's turn, any migrants with the same profession as your guild would automatically join your guild, adding a 1 "forum trade point" to your total, all the others are left to fetch/carry stuff and are given the "farmer/brewer" skills. At the end of the turn, a Player sticks all of their guild-members in a squad (or squads) labeled "<profession name> guild" and makes them "sleep in barracks at need" and training all year long, before zipping up the save and passing it along. Any increases in "forum trade points" are tracked by simply looking at the "z" menu and finding the number of dwarves in one profession or another, then adding the amount of points traded in the forum (a positive or negative number next to each Player's name in the turn list)
Ex:
3) Timeless Bob (-3)
So I've spent three of my points. If my members are 12 rangers, that means I have 9 points to spend or trade with if I wish. Easy.
Here's the guilds as I see them:
Miners
Woodworkers
Stoneworkers
Rangers
Metalsmiths
Jewelers
Craftsdwarves
Fishery Workers
Engineers