Concentration seems to be unavoidable. A direct consequence of the power law respectively Matthew principle. I haven't researched the alternative PoS (prof of stake) concept too deeply, but I'd wager it'll end the same way.

This isn't a technological problem, but a fundamental principle of our reality. Still, the ability to fork and just restart the chain from a previous point, with new miners, gives the collective some choice on a fundamental level, should the concentration ever become a problem.