I've seen them in trade binders before, but I've never seen them in play (the only exception being a Booster Tutor in a friend's cube)
Some decks will occasionally feel fine skipping their combat step, but nobody wants to skip drawing a card or getting to cast spells
Even among obvious contenders, classifying what sort of card earned its place on the Game-Changer List spotlights Commander's most important fundamentals (card advantage, resource denial, fast mana, etc.) while also directly listing what strategies, most often end up winning games
On top of the standard sets, look for more crossover sets to come in the form of the Universes Beyond product line
The Aristocrat requires you to have other creatures in play so as to negate the single toughness and be able to really abuse all aspects of the card
You can also shield your key creatures from the worst interaction with premier equipment like Champions Helm, Commanders Plate, or Sword of Feast and Famine