I suppose what I said would be less of an issue for cosmetic items, good point. As for “how to get other games to recognize the tokens for the cosmetic items”, I suppose one reason could be via the use of copyright: grant a license to other games to use the assets for the items, conditional on the requirement that they only allow it for people who have the token in question. If they are high quality assets, and in a format where they can be easily incorporated, then that could make it worthwhile to implement them. Of course, the game using the assets from the other game would prefer to be allowed to use the assets for anything they want, but, seeing as it is essentially for free, if it fits with the art style and setting/mood of the borrowing game, that could make it worth it, maybe. If the group granting the license wanted to provide additional encouragement to do this, they could also issue some number of the tokens to be distributed by the other game. This could maybe work as a cross-promotional thing. People from the first game which don’t have the token could be motivated to try the other game because they can use(wear) the item in the game they already play, and people who are playing the second game could be made aware of the first game by the introduction of the item. (Of course, many parts of this could be done without any sort of token by just having the game servers contact each-other on occasion, but tokens could allow the sharing between many games more easily maybe. Also allows making it really be the same item on both games such that if one sells it in one, it is also gone in the other, without needing the servers for the different games to constantly contact one-another over that kind of thing.)

I do think something that could be interesting would be to use a permission-ed authenticated append-only database (essentially like a proof-of-authority blockchain, except not necessarily a blockchain, could be closer to an ordinary database), which could allow the kinds of cross-chain trades we see in actual blockchains, which could facilitate trades of items between different games, without requiring the players trust that the other player will uphold their end of the trade on the other game, just trust that the game servers don’t cheat, as the game servers would have basically no reason to do that. I think these would be able to scale much more easily, while still being potentially compatible with actual blockchains.

That's an interesting idea. Cross game cosmetics would be especially interesting if certain items were not made available for sale by the developers, but had to be earned via in-game accomplishments.

Ex. if you kill the final boss in the game, you get a hat that you can sell, but every copy of this hat was earned by someone who beat the game.

Could be an interesting way for game studios to cross promote - if player of Game B wants that fancy hat, they have to either beat Game A or trade with someone who did, incentivizing more people to play Game A. Some number of people would be swayed in which games they chose to play if they could 'cash out' once they were done with it - even if it's only ~$20 for dozens of hours.

So this could be used to not only bring in revenue, it could alternately be structured to build audience.