Why not just sats? Bitcoin works fine with LN and removes a native shit token from the start. I think the challenge is really creating a tamperproof system to prevent the duping and other abuse that affects the economy of an MMO. The currency is just that, currency. If every unit of ore and every module created for a ship has to be verified by an internal ledger then you've already fixed one of the biggest economic issues in MMO's

Specifically, I mean that game items could be attained through POW. An example would be crafting. Other items could be committed to this crafting operation as ingredients (referenced as preimage tags). The POW (NIP-13) yields a new item that required other items and energy to produce. Since its a game, you can require events to be published to the game's dedicated relay. This allows the game clients to check for double spends on ingredients. I'm working on a game that uses a system like this. The event ID of the item must contain leading zeroes, and the digits after the zeroes must match a certain bit suffix to yield a particular item. The game functions as an interpretation mechanism for POW. Game items could also be purchased for sats. Crafting and buying are different things.