I think you're gonna have to be a big player that can order large quantities from TSMC / GlobalFoundries / etc real soon. But I'm not worried for mining, in company-terms it is low entry, designs are very simple compared to gpus/cpus. I just hope that economy of scale doesn't somehow give too big of an advantage and we end up with three-four mining cos, that would be a disaster for bitcoin to the point a protocol change might be necessary.

As for concentration right now, imagine what a high rank Chinese politician could do to bitcoin. Is it possible to see how much mining there is within China's borders somewhere?