As far as Mitchell is concerned, I wouldn't be surprised if the character makes at least a brief appearance and/or is mentioned in passing. The role need not be a major one, nor even a speaking role, because fans-in-the-know would know who he is and what he's destined to become...
Exactly...Kirk, sitting at a desk in front of a classroom, rises to greet an approaching Professor, dismissing the lower classman seemingly being kept after class with "Try to keep your mind off the ladies and on the lecture, next time, Mr. Mitchell." We'd all fill in the rest and the non-fans wouldn't give it a second thought.