Since we have some serious utility holes in some of the GM abilities, I was thinking of emphasizing the ability of all GMs to serve as trainers like the military orders do.
The way I was thinking about it, the GM could get a new task "Assist a Guild Member". While the member was actually performing the task (smithing, mining, sparring) the GM would provide an xp multiplier based on the difference in their skills. So a Proficient GM might only be able to give a 10% boost in xp gain to a novice, while a legendary GM could double or even triple the xp gain for the same novice.
The GM would also gain a little xp (you learn a lot by teaching). This would help keep the GM at a high skill level despite the fact that he/she is being frequently drawn away by other tasks (meetings, office work, training) or even having the labors removed to free up time for guild business.
This would also promote the creation of "training" workshops. Set them Guild-Only, with a skill maximum set just above the "students" (or even set specifically to a student). Set a job to repeat and only the "students" will come to work there. The GM will then "help " them.
It could also be possible with some guilds to limit the GM's training area to just within the designated guild hall. This has an added benefit of making it more likely that the Guild Hall is built near the actual work sites (to save hauling from input and output stockpiles).
The downside is that it is unlikely, even with (or because of) GMs selected based on highest average skill (all the skills the guild governs), that the GM is the best possible choice to train someone. The GM might be a legendary cook, brewer, and thresher...but have absolutely no skill at milling.
The above point might lead into an area of discussion I at first scorned, but now think might make a good appendix: A more detailed Guild structure including Journeymen/Masters.