[DennisP]

Ethereum just had a brief encounter with that threat. It's switching to a system that burns most transaction fees instead of giving them to miners. The miners took exception to that, and made a lot of noise about a "demonstration of force" in which at least 51% of them would move to the same mining pool, showing they could attack if they wanted to.

The rest of the community called their bluff. The miners backed down and the change is scheduled for July.

Miners don't have that much power because if users, apps, exchanges, data feeds, and tokenized real-world assets are all referencing the new hard-forked chain, then miners have a choice between running that fork or going out of business. A chain with just miners has little economic value and can't support all those GPUs.

Under proof-of-stake, a 51% attack is even less of a threat. A double-spend attempt results in destruction of all your stake. A long-term censorship attack could be maintained, but if it's egregious then users could remove your stake with a hard fork, and if there's support for that from all the above entities, it'll work.

Miners and stakers are not governors. They're service providers.