Let me see if I understand you correctly by comparing it to something I think is similar in my favorite single player game, TES3 Morrowind.
Nearly every NPC in the game had the dialogue option "my trade" where they would tell you their class, what they do, and what skills they use. For example, a knight would tell you they use long swords and axes, wear heavy armor, and train in speechcraft and armor repair. Also, every class would point you to one person who could tell you more about that class if you wanted to learn. That person would be able to tell you about all of the skills involved in that class - the different types of longswords in the game, how to perform armor repair, etc. Some would also tell you who could train you in the skills involved in the class.
Basically if I understand this idea right, it would be similar for the NPCs, and players would be able to pick a class or change their class if they want. And NPCs would address them by their name and class.
It seems like this could be incorporated into the already existing factions system in the game. Members of the food association could tell you where to get cooking/baking training, crafters could tell you where to train smithing or whatever...