How is the adverse scenario you describe different from a plain old 51% attack? Each proposed protocol change where 51% or more of the network can potentially game the rules and break the system should be considered just as acceptable/unacceptable as another.
There comes a point where some form of basic honesty must be assumed on behalf of participants benefiting from the system working properly and reliably.
Afterall, what magic line of code prohibits all miners from simultaneously turning all their equipment off... just because?
Maybe this 'one':
"As long as a majority of CPU power is controlled by nodes that are not cooperating to attack the network, they'll generate the longest chain and outpace attackers. The network itself requires minimal structure."
Is there such a thing as an unrecognizable 51% attack? One where the remaining 49% get dragged in against their will?
Daniele