One for which a lot of demand exists is a better Commander for Werewolf than
Ulrich of the Krallenhorde. Perhaps something like
Immerwolf, boosting wolves and werewolves while stabilizing werewolves in their stronger form. Making a Commander that triggers whenever another werewolf transforms would likely get overpowered rather quickly...
What I would like to see, personally, is an Aetherborn Tribal theme. It is a unique race, with an interesting culture. I could definitely see it being a mono black deck with either an artifact subtheme or a +1/+1 counters subtheme...