I'd think something similar to the old mechanic would be fun in the future: a prince may choose any class he wishes to pursue as an adult, but if he ever gets recalled from court and switches to a different class, he must relearn all skills in that class once again. It would make sense for the game to store their learned skills per class, so that if you switch from Marshal -> Merchant -> Marshal again, you'd still have all your past Marshal skills.
This could be a tough request for the devs to work on the current game though. It looks simple enough if we're looking at it from the player's perspective...but how would it be handled by AI? Would they keep swapping too? Then there's the puppet status (e.g. bribes) too, and more. So this idea might be better thrown at a potential KoH3 instead.
Also, rather than family interactions, I wish the royalty could also have more actions with their people instead. Right now we could only hold feasts during childbirth. Royalty-Exclusive missions/actions that could please the opinions of people regardless of their class could be a nice addition to the current selection.
Additional actions, skills/slots, and more might be added by the community instead, so my hopes are the devs place their attention to better mod support instead.