They're powering down the whole amount and getting 2.44 million STEEM per week.
https://steempeak.com/@binance-hot/transfers
Binance and Huobi are in full powerdown. Poloniex, owned by Sun, is not. @poloniex has ca. 2.28 million SP, which equals to about 4,476 MVest. It is currently not voting on witnesses, but if it did, the below picture gives you an idea of what it could do:
It seems that by using @poloniex's stake alone, a supermajority is not achievable.
If you want to know who's voting on which witness, click on the megavest number after the Steem version number on steempeak.com/me/witnesses (see the above image). Interesting names may crop up...