Totally agree - this will only happen if it makes economic sense for the developer. Big companies like Blizzard won't bother since they can build and manage their own marketplace, but smaller developers who can't afford to do that will still be able to unlock value by participating in an open market.

Players re-buying the same item is definitely profitable, but it may turn out to be more profitable in the long-term to allow players to freely trade items while taking a cut of each transaction as royalties. Also, as mentioned before, NFTs allow for single-use items. A game could provide all sorts of different items with different rules.