I think Mage Order can serve as an alternative path for mansion upgrade progression to the slaver guild, since right now the order is only there for the main quest despite it supposed being an influential organization in the world.
The Mage Order repeatable quest could be something along the line of brewing specific potions, or go out in the wild and hunt down fugitives/wanted criminals. It can be a good alternative to players who either want to roleplay as hardline 'good' character (a bit oxymoron for a game revolved around slavery, I know), or have a tendency to get attached to the slaves they own and don't want to sell them to get upgrade points.