I made an Etrata, the Silencer deck, certainly qualifies as niche. unfortunately this pandemic thing happened before I could get a game with the deck.
My favourite commander is Glissa, the traitor she hasn't seen much love since they started printing super powerful GB commanders better suited to traditional GB play styles. Glissa, remains a strange mix of versatility and limited. where a lot of the best GB stuff tends to push hard in specific directions glissa gets all the versatility that artifacts give you, allowing her to basically do anything at the cost of not being able to maximise the way other GB commanders do.