In theory it makes it possible for other games to use the same items to make stuff in their games (I doubt this in practice)

I've heard this before, but there's literally nothing preventing games from setting up some shared items on their own without NFTs. Nobody does it because companies want to keep their IP, and worrying about external items would be a nightmare to balance.

NFTs solve like 1% of the problem of sharing items. So much more goes into making them actually work. For example: NFT id 5551337 is owned by the player: now what? How do you figure out what 3d model to render? What actions can you perform? How does it integrate with other systems? All of that is going to have to be custom for every game involved on a per-item basis.

There was an abstract conceptual theory of system agnostic game add-ons. It isn't... completely inconceivable.

You could work with a relatively prolific engine, like Unreal, and set up a standard character model dummy with designated hard points for attaching accessories and certain default movements. Then any accessory could simply scale to the environment - Master Chef could swing a keyblade while the Elden Ring guy gets to wear Iron Man armor, because these are all "human" models with well-defined structures that could map to the associated equipment. The blockchain becomes a universal registry for these assets that a platform can read from to render the art.

The problem is that nobody ever actually implemented this universal protocol. They all just ran off making jpegs of weird animals and running fake auctions to create the illusion of a secondary market. You had zetabytes of data being processed so some Baked Alaskahole could claim his Kumming Koala was worth $40M.

I don't even strictly begrudge "the blockchain" as an idea for licensing and data storage (just please don't ask me to think about who is generating the licenses or storing the data). But it was all vaporware. None of it was anywhere close to being created, much less delivered. People were throwing billions with a b of dollars at entirely empty promises.

Collectibles are non-fungible tokens by definition, and blockchain is just a data structure.

I don't care about collectibles / NFTs, but this is nothing new in the gaming world.

Thing is, none of those advantages are real either, compared to a public database and API. Steam's inventory API already maintains items beyond the lifetime of games, AND you can use items across other games. You can't manipulate the Inventory of other games but I bet if there was demand (there isn't) this could be implemented easily.