You can't control what miners do, sure. But you can fork code that changes the game for them.
Contrary to all the noise, Bitcoin does not need commercial miners. They are parasites. Allowing them to dominate mining was a serious bug. It's users who should be mining.
I mined a little in the early days, but it kept my CPU pinned into the red and frankly all the people online patting themselves on the back on the size of their mining operation were offputting. I'm interested in cryptocurrencies because of their potential to liberate the mass of people from financial bullying by governments and corporations, not as a speculative vehicle to easy riches.
This will seem pointlessly ideological to most people, but I'm struck by the fact that the bitcoin blockchain is held up as 'proof of work.' There's no work involved besides that to understand the system initially and any code contributions made to the source tree. The actual calculation is carried out by machine. So mining is basically a game for capitalists to invest in industrial hash table production. People who learn about it later and comprehend it in full but don't have any large sums of capital to invest in mining equipment or as a speculative investment don't really derive much benefit from it.
Don't get the idea that I consider it a bad thing because of this - its mere existence speaks to the fact that we've run out of accessible natural frontiers where the curious might stumble upon a fortune, and so we are forced to invent them.
It's not about need. If it is profitable to mine, professional miners will exist. You can't create an incentive structure and then call it a "bug" when somebody optimizes for it.
One could limit share of hash power. Perhaps by IP address. Or through blockchain links to previously-solved blocks.
The Tor Network, for example, has mechanisms for excluding bad participants. There's the bad exit flag, for relays that snoop traffic. Relays that harvest onion hostnames get banned. So do relays that attempt traffic analysis.
There's even a policy of discouraging new relays in commonly-used AS. There's no exclusion mechanism. But I don't see why there couldn't be, if there were too much concentration.
Contrary to all the noise, Bitcoin does not need commercial miners. They are parasites. Allowing them to dominate mining was a serious bug. It's users who should be mining.