Ignoring for the moment that i am suggesting a slowed peg, and that that is exactly what drivechain a can do...

I would if both distance and incentive are at play. A galactic economy based on earth at its core and earth bitcoin, would have to eventually settle in earth bitcoin, but local currencies, colored coins, fiat IDGF would be more available . Bitcoin as final settlement. God can you imagine the fees.

Even if the distant miners were to try and mine bitcoin and somehow use an excess of cheap energy over there to profit here, the distances already exclude any excess amount of energy far from earth from competing with earths miners.

Put another way, c means there is a cost to transporting that information back to the earth. That miner has to expend energy to escape the blue giants gravity well, then travel to us, all before we have significatly upgraded our own miners in the time it takes them to get here. Space-time arbitrage might happen, but not fast enough to cause insecurity in the main chain.

Actually that is an extremely interesting attack vector. If our entire civ was based on expesive energy and someone started broadcasting cheap energy bitcoins it would kill the economy. lol

This is all assuming sub FTL obviously.