1. More scripted interactions: I really enjoyed having various paths to solve a problem/situation and thought that these interactions are a nice way to make areas of the map more memorable.
2. Improved stronghold: as is, Caed Nua feels very static once you finish upgrading it and the various visitors are very flat. As has been mentioned in other threads, I think that populating the grounds and the keep with more NPCs (guards, labourers, farmers, merchants, stewards, etc) would go a long way in giving more life to the stronghold. Moreover, you could add the scripted interaction mechanic for random events concerning the stronghold and its surroundings as well as to give a sense of progression.
3. Banter with companions: when companions banter amongst themselves, have the possibility to have a conversation with them concerning the topic discussed. Does not need to be anything too in-depth, but to show that even aside from the main storyline and the side quests you find the time to engage in some light chatter with the people who have been following you around for months.