I miss the mentor system from back in the day. I always planned to make my chars mentors when they were old and grey, and write books. The latter of which I always thought was one of the coolest things about the mentor class.
I'd suggest the following, to make the mentor class more attractive and to encourage its use across all realms:
Make it similar to the Ambassador position in that it is a realm-assigned role and not a subclass. This will make it more attractive for players who also want their chars to be heroes/traders/diplos/whatever, also enabling new players to learn about those subclasses from those who actively play as them.
Figure out a good ratio of mentors:total noble count and implement some form of incentive to get realms to assign the position accordingly, with each realm no matter how small having at least one, and increasing the total number of mentor "slots" according to the size of the realm.
Allow new players to select mentors on each of their characters within a certain time limit. Have a system where their different options on each character come along with some kind of metrics showing who is more active, who is more active in direct messages to their students, who plays what class(es), etc. This will enable new players to choose active mentors involved in the classes that interest them.
