I would love to see an option down the road to complete a quest line involving the collection of reagents and killing specific people for their blood/souls to be able to summon a loyal demon companion. Something more impressive than the ape demons we get.
Alternatively but along the same lines for those necromancers out there a quest chain to assemble a Skeletal guardian. Perhaps force an ancient renown warriors soul into this new undead body.
Just a hope for future expansion of the companion system.
May Set be with you