I would like to see pet paper-doll UI to adjust Soul pets in stats and looks, some extra added customization to pets. Paper-doll detail slots to add bonus to Rift types, damage, HP and looks. This could also expand to familiars.
I normally have a class that uses a pet but I think would be nice for all souls that aren't pet based to have a pet/familiar of some kind. This would open more play with the option to have a Familiar in use over a pet in some cases and 3 choices regardless of Class and soul build. Could be a non-attack type but something that would give bonuses to the owner and/or group and limited to 1 pet in use like having an Elementalist and Necro souls with only 1 pet in use at any given time and suffer death from attacks and damage. Can be uncontrollable type that follows it's owner but also something that could be a target.

Recap:
Non-Pet Souls get a Non-controllable Familiar
Paper-doll UI for Pets and Familiars
Pet/Familiar Paper-doll Slots for Bonuses - Rift types, Damage, Healing, stats Etc and looks.