Hash rate is part of the 51% attack problem.
Which isn't a problem, so doesn't need to be fixed.
I think you may be underestimating the dangers of mining concentration.
My latest book-mark:
How A Mining Monopoly Can Attack Bitcoin- Loss of decentralized trust narrative, inability to differentiate Bitcoin from competing technologies.
- Double-spends against 6-confirmed transactions are certain to succeed.
- Selected miner targeting: Pool can reject any selected block found by any competing miner.
- Selected transaction targeting: Pool can reject any selected transaction and keep it out of the blockchain.
- Selected address blocking: Pool can block Bitcoin flows in or out of selected addresses.
- Transaction Differentiation: Pool can deprioritize certain transactions and rely on other miners to mine them unless a (hefty) fee is attached.
- Fee Extortion: Pool can deny transactions from a particular address unless a (hefty) fee is attached to those transactions.
- Complete denial of service: Pool can ignore and orphan every single block found by competitors, thus stop all Bitcoin transactions.
I think this sums it up nicely. There are lots of things a 51% pool can't do, but there are also a lot of non-armageddon type things that it can. The hacking distributed guys have done a good job laying things out and make a pretty convincing case that bitcoin isn't decentralized if a single entity is at 51%.