Thanks for sharing this.
Are polo and bittrex the only exchanges for steem? No, in this page
https://coinmarketcap.com/currencies/steem/#markets
I found for example "livecoin" as annother exchange. But - there is no account for livecoin. That's surprising for me. The next possibility to trade steem versus BTC is of course blocktrades. If I understand the blockchain of steem in the right way, everybody who owns steem has to have an account.
By the way, the reason for the blocked transfer from and to poloniex is still unclear.
So many questions, I know.
and blocktrades does do instant transfer
Livecoin's Steem account is @livecoin.net. They own only 57,612 so I've left them out of my calculations.