The scenario sounds extremely implausible; a chain with 90% colluding actors would be worthless, and the remaining 10% of honest users would likely exit to another chain that is not majority run by malicious nodes.
For example: migrating to a new chain ID and restarting with a validator set limited only to the public keys of the 10% who are acting honestly, and loosening that restriction slowly over time.
The attack would end up being extremely costly: not only because it makes the original chain’s token price worthless (who wants to be on a malicious chain?), but because the attacker may also have their deposit slashed in the new chain by the now-majority of honest users defending it.
The 90% is an arbitrary and unnecessary figure. Note it is not 90% of actors either. It is the bag holders of the bulk of the wealth. Far easier to imagine. And if you try to fork off into a world where the most important financial players have nothing, you will not be taken seriously. The money is more important than the crypto.
For example: migrating to a new chain ID and restarting with a validator set limited only to the public keys of the 10% who are acting honestly, and loosening that restriction slowly over time.
The attack would end up being extremely costly: not only because it makes the original chain’s token price worthless (who wants to be on a malicious chain?), but because the attacker may also have their deposit slashed in the new chain by the now-majority of honest users defending it.