More Servant Functionality
Perhaps adding a button where you can ask a servant to follow you like an ally and fight with you (maybe you have to "rent" them out like this for a blood essence cost). If they get downed, the recovery time can be much more than it currently is with getting injured on hunts. It would be fun in PVP to have you and a servant or two fight against another group!
Also being able to ask them to stay in a certain room, or "pin" them to an area they protect. I really enjoy having a room for my servant caskets and it would be nice to be able to set them into defensive positions easier. Maybe when they are pinned to an area, they can automatically loot things on the ground making pseudo automation for crypts and such?