The ability to trade, sell, and own game items (weapons, trophies, powers, property) could be massive.
This is the dumbest fucking use for a blockchain besides all of the other dumb uses. There is absolutely zero financial upside for a developer to support some in-game item purchased from another developer. It's all cost with no benefit. Epic isn't going to spend a dime to support a TF2 hat in Fortnite. Valve made the money from the sucke...customer, not Epic, which means Epic is out the cost to support the item in their game.
If Epic charges to import the item to their game/platform, now you're paying twice for the same "item". That's worse than paying for it once.
Even if you decide to pay for all that artificial scarcity there's no guarantee an item or any in-game asset has any utility between games. A jet pack from a sci-fi MOBA is meaningless in a fantasy MMO. Mapping assets between different games would be a huge intractable problem.
That's to say nothing about the copyright issues. If a game let you import Mickey Mouse ears into a game they would be inviting a nice fat lawsuit from Disney unless they had a prior licensing agreement.
Using blockchains for in-game assets would be a compatibility nightmare, a copyright disaster, and a giant money sink for gamers. What an awesome fucking idea.