A sequel where a ship, or rather a fleet, serves as your stronghold equivalent, and a much more central mechanic, with composition of ship types and acquisition of said ships varies things up.
This would simultaneously provide a money sink mechanic that would allow the misers in the development team to do away with the god aweful turn mechanic of the stronghold, as a fleet of ships would need constantupkeep with which any regular monetary gains can be balanced against. Or maybe a need to go on regular enterprises/raids to flsuh money into your pocket which is then trickled away by the passing of time, giving an opportunity for randomly generated "vocational quests".
Ships would also allow for travels around much of the world we only read about, connecting varied biomes to explore.
Personally, I would hope of a return of the watcher aspect, because the game sometimes shows that this ability can be much more perfidious than it would seem most of the time, ****ing up peoples souls and past lives for your own perverse amusement or selfish gain. Not to mention that the way you can deal with maerwald suggests some kind of soul-absorbing aspect for power, which is always awesome, or at least the option to choose between doing the decent thing or being a powerhungry prick and many steps in between.
Another idea would be to form companions not in the party into a secondary/tertiary party of, say, 4, which is tasked with all the side activities the stronghold provides, and making the composition more important based on background and character, for instance: having the task of trekking through the wild to meet with glanfathan tribes and parley would be a task for hiravias as a glanfathan, sagani as a ranger and kana for his general tact and sagacity, as opposed to pallegina who is city folk and durance who is repugnant.
This would give a reason to change party composition regulary and also make every companion well equipped, not just the A-team.
Coupled with the more unexplored but hinted at aspects of soul-****ery you could control these parties through soul projection or the like after they arrived at their destination, making the alright "parchment-adventures" culminate in the usual gameplay. reading about how a companion descends donw a well to face a colony of wichts is okay, taking control of said companion with own little party would be much more interesting, even if just for a single dungeon.