Thanks for sharing this.
Are polo and bittrex the only exchanges for steem? No, in this page
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.
https://coinmarketcap.com/currencies/steem/#markets
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.