At some point, it becomes a political threat. They already control 5% of the BTC supply. Let's imagine a hypothetical future where they control 25% of the supply and then get hacked for everything. Since their custodial holdings represents such a huge portion of BTC investors, there will be huge financial and political incentives to destroy Bitcoin's immutability and roll back the chain.
Sadly, markets usually become more consolidated over time, not less.
hmm..
as far i know , to do re-org require pushing for consensus from major miners and mining pools to gather over 51 percent of the network’s total hashing power , and i guess its not a easy task.
but,since 25% is not a small value , probably miners will do it, but negative effect such as credibility for bitcoin will lose.
and i am sure , after it happen , people will lose interest.
but well, the only good thing about this is that cold wallets have very little chance of being hacked.