Well, I havent done the maths but I guess you would need at least half of the total steem market cap, so around 115M, but we could always fork it and run a different chain, so not sure if the efforts will pay off.
Same goes for huge BTC mining operations.
Bitcoin is already controlled by miners, chinese miners.
Pocket change for the people robbing us all our lives, that's why I like all the new up and coming coins like steem, if we lose control of some just move into another. Someone will figure a perfect scenario some day, might even already exist. where every wallet is equal and no double dipping. we all share equal and grow together. After all it was meant to be currency in the first place. BTC is no longer that, but a store of wealth like gold or silver and that's fine. grand daddy didn't ave it right, but we are building on the platform :-)
Cheers