Collectibles are just a subclass of Commodities which can't be taxed using Mark To Market rules, but there are a whole host of commodities which are just like that. Precious metals, rare coins, cards, comics, etc., are all collectibles, but they are still commodities for regulatory purposes. For example, here is PR release of a CFTC enforcement action against some fraudulent coin dealers: https://www.cftc.gov/PressRoom/PressReleases/8694-23

IIRC, the IRS and CFTC have already issued rules to treat NFTs as collectibles.