Arkand's idea is really interesting and makes sense. Maybe each elemental or any creature in the shelter plane could give us a side quest that would permanently boost some of our skills/stats/etc. Maybe, instead of stats, some side quests could reward us with really unique legendary item.
Just to have an extra skill/spell book vendor is somewhat boring.
Also, any chance to add more storage chests in the shelter plane - so far i think the only one available is in the heroes hall and it can hold 20 items. For those of us hoard ingredients for later in game use that is not enough space