My own lil custom 40 card format is actually explicitly designed to be backwards compatible with any existing commander deck! You can just take a deck, draft from it (or just split it down the middle after a good shuffle), give one of the decks to a friend, and start playing!
(I still want to make a Commander deck which can be split in half, have one or two Commanders added, and work as a Tiny Leaders/Duel Deck pair)