I suppose that is the Real Threat to Steemit in future... Pooling out the money and investing null is going to be hard challenge for Steemit survival, else there is some infinite reservoir of Steem.
Poloniex already have been so scamy; crashing, hacking, what not has happened to it and still people are going for its lucrative exchange rates. I suppose the Poloniex maintains that Lucrative Exchange Rates by its scamy habits, else it should be running in losses.
I am not saying that one shouldn't cash out from steem, but if you do so why don't do it with someother exchange which helps both you and steem(to maintain its value). It is like "killing the Golden goose with thought of taking all the eggs". Better be patient. Why not invest on some Steem and harvest the crops for longevity.