There are a number of well known undesirable effects of mining pool centralization, primarily:
- increased risk of collusion
- a small set of pools effectively gain veto power on the evolution of the main net
- a big proportion of hash power may fall victim of targeted attacks, and possibly hijacking (of the mining pool, and ultimately, if the pool is large enough, the entire network)
This issue was acknowledged for example in this blog post. It is therefore rather surprising to see that the Ethereum blockchain is no less centralised (approx 50% hashrate controlled by the top 2 mining pools over the past 24hrs, for example) than the Bitcoin counterpart.
Other than the eventual transition to proof of stake, what actions is the Ethereum community taking to counter the mining pool centralization trend?