I was looking for some ETF news and apparently the VanEck one will pledge 5% of earnings to "Bitcoin core developers" during the next 10 years from the money they'll make on fees.
I imagined an hypothetical scenario where there is a massive hack or some sort of a disaster scenario where there are massive losses, and now those same good samaritans that are funding developers start pushing a campaign to engineer a rollback of the blockchain Vitalik style. What would happen? If in the future ETF holders become the 99% and 1% are self-custodians, then it will be on their interest to push this agenda. What if they have enough % of developers under their payroll, and enough people supporting it because they lost their money, and start pushing for a hard fork? What would be the game theory outcome scenarios at play here?
This could be applied to any other narrative to come up with a hardfork. Like, BTC pollutes the environment, let's go to PoS, or this and that. But the one I could see coming, is seeing a massive loss and then angry people wanting a rollback and start campaigning to pass laws that force developers to do this and so on. Most custodians are using Coinbase, but some will be self-custodians, Fidelity being one of them. I expect their efforts to pass such hardfork to fail, but who knows if like I said, most people in the future depend on ETFs and start pushing for laws to "protect investors" that force developers and miners to do rollback plans and so on. This sounds ridiculous now but you never know.
Why are you thinking about ETF's? Have you forgotten that Bitcoin is not an ETF?
And neither is it Ethereum (thank Satoshi!)
ETF is just a very important tool for more Bitcoin adoption.
Your disaster scenario is impossible, as many others have already pointed out in detail. No further need for explanation. Bitcoin is awesome, decentralization is awesome. Blockchain is super awesome.
Actually I think the scenario described in the OP is perfectly possible if enough custodial Bitcoin services (ETF companies, exchanges etc.) collude and the community is so indifferent towards Bitcoin's original "values" that it accepts it.
Developers on a payroll can be an element in such an "attack". Not because of the needed skills for the code changes, e.g. to roll back a transaction (I think that even I could do that, even with VERY limited C++ knowledge), but because of the influence of renowned devs like the current Core group on public opinion in the community. We've seen that already in the block size debate. I think if most Core developers hadn't taken such a strong stance for Segwit and a restrictive block size policy, then the current "Bitcoin" could actually be BCash or even BSV (which in my opinion would have been a much worse outcome).
Miners will follow the chain where they believe the value "is at" - if there are several options, they'd chose the one they think the community as a whole would pay more money (or other values) for a coin. Here, colluding services providers could be a big problem, not only because they directly demand Bitcoins, but also because they have also influence over the community's "collective opinion", above all over the more indifferent part of the Bitcoin users - those who only want to invest in Bitcoin and don't care that much about the deeper qualities like immutability.
However, if there are enough influencial voices in the community insisting exactly on these "deeper" qualities, then I believe the "attack" would fail, like BCash failed.
I think you might be underestimating the scale of the attack. The amount of payroll money alone.... How many people would you need to put on the payroll and for how much money? How decentralized does something have to be to make it 'technically impossible' to attack in such a way?