Would you be so kind and offer similar approach they did in Star Wars the old Republic, not saying you should copy their approach. Every Game can inspire one or some feature. I believe it was a win.
- A complex relationship,tons of dialogue as is often in ESO.
- Romance,marriage option depending on race , same sex.
- The ability if humanoid race to pick let us say each of them current 10 races as companion regardless of characters' race.
- More exotic variety if possible.
- Do not make it insane grind or ages let us say if your companion has a level if should level automatically with you
- Companions should not be used to have major advantage in combat giving healing boost or taking care of enemies,game is later on already enough easy
- Switch between RP / Combat mode. Disable companions combat on/off by default in settings