Honestly, I'm probably not going to have much luck implementing this (I've had enough trouble implementing a Java blockchain reliably and an Infiniminer voxel engine by themselves), but I might as well share the idea
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While this might end up as little more than a gimmick game, its handling of crypto-currency could potentially integrate with real cryptocurrency like Bitcoin or litecoin through valuable game materials being bought and sold.
Basically, the point is that one can "mine" resources within the game and use said resources in order to work on one of multiple "worlds", which would likely be similar to Minecraft-like worlds. As the client mines a series of merge-mined blockchains corresponding to various types of materials, whether in a pool or individually, they will get materials and tools such as coal, iron, and the like.
In addition, things like crafting and smelting will occur where a given set of coins corresponding to, say, coal and iron, are destroyed and steel is created in a transaction (in its own blockchain corresponding to proof of work of smelting/crafting).
Land can also be obtained by mining one of the blockchains. As you get coins you can spend them on land. This land would then be only usable by a given private key, unless that key is shared or a one-of-n multisig is set on that land.
Any coin, at any given time, would either be in the inventory or placed. When in the inventory, it would be spendable as a regular coin, while when it is placed it can't be spent until it's moved to the inventory address before becoming spendable.
Instead of tools being used, tx fees would apply to placing and removing blocks.
All chains would have relatively fast blocks (15 seconds), and varying rewards based on the commodity they represent.
The client would also include a 3d voxel engine for rendering the world.
The terrain would be generated through perlin and a pre-defined seed. Since anyone can pick any unclaimed land there's no real need to justify a seed too much. That being given, people will still need to mine in order to be able to pay fees even if they use the free dirt and stone they find on their plot. It would be the one commodity that would be generated upon buying land from mining landclaims, instead of being mined directly.
If you have comments or criticism (even if it's just "this will never work, you're a nut job") feel free to reply.
