It will actually be staked currency, not outstanding, and it's more than 51% because Eth2 is sharded (64 shards at the moment) and randomly selects committees t

It will actually be staked currency, not outstanding, and it's more than 51% because Eth2 is sharded (64 shards at the moment) and randomly selects committees to verify blocks, so you'd need to hold enough validators (each holding 32 ETH) to guarantee a majority in a randomly selected committee for a block. And the Eth2 genesis won't occur until a sufficiently large amount of validators are active on the beacon chain, so you can't hijack it by investing large early.