Have you spoken with the Diaspora team? This was their exact idea, until they started implementing, and the practical concerns moved them back to the client-server, node-based model.
You don't always need a singular, damning situation in order to prevent a model from being implemented. Sometimes dozens of purgatorial ones are plenty.
Using the CPU power of a device that is capable of playing video games to calculate your social graph (that is stored on that same device) is extremely powerful and well worth the time and dedication.