I think that there's very little variety when it comes to summons/combat pets, and it's quite monotonous seeing everyone with the same thing. Since actually adding new summons/pets would require many balance changes, a safe solution would be to add skins or even models for each existing summon/pet. This would allow for a much needed user customization and variety.

The skins/models for the Twilight Matriarch, for example, could be another winged daedra, to keep some consistency and to avoid confusion.