We can already customize the keep to a degree with the painting frames and the individual rooms being opened as we level up the Ubersreik five, but I think it could be further improved if we could change things a little further. Specifically, being able to have a seasonal/holiday theme equipped whenever we wanted, and for our favorite bunch of heros, rooms that could match the themes of our favorite careers.
A quick example: Bardin’s room has just a few things for a ranger veteran, bow, beer barrels, work table, but in the Outcast Engineer’s trailer, they actually gave it a one time makeover, with more steam pipes and blueprints, so maybe we could gain the ability to redecorate it that way ourselves.
Now as to how I think it could be added in-game without disrupting the balance, as of right now many of us probably have more scap and magic powder from salvage than we know what to do with, so perhaps we could use said salvage to pay for keep decorations?