This is one of the problems with proof-of-stake, although the attack manifests differently and is much slower. Someone can borrow money, and pay higher yield than the normal staking yield, to buy staking power and change the rules to their favor. It's already happening and most people are staking through exchanges, instead of running their own staking nodes. It's a fundamental failure in the PoS incentive structure, and that's why it's inherently more risky than a proof-of-work system.
