I had similar thoughts. Hypothetically, the "center of mass" of mining could drift to a point in between Earth and Mars: perhaps an enormous train of miners sling-shotting between the two planets.

That would only work for these two planets, though. @Scoresby's underlying point would still hold if we switch our example to Io or something else further out in the solar system.

Undisciplined

Unfortunately, there's no way around the speed of light. 

Scoresby

bitcoin

Should Mars have its own Bitcoin chain?

What if there is a node/miner/watchtower in space somewhere in the middle between the Earth and Mars? The time to get to this middle point would be half from both planets. There can be more such floating nodes on 1/4, 3/4 of the distance to increase decentralization, reliability and probably even trust.

(Just thinking loudly.)