Justin Sun did a 51% attack for sure. He controlled more than what is necessary to have absolute control and he is exercising it. This has nothing to do with consensus is exactly right.
A key thing to highlight
If Bittrex follows through by following consensus they are idiots.
If there is anything that I have learned from being in the crypto space, all exchanges given enough time turn out to be scammers or get hacked or "lose users funds".
Some exchanges have a better reputation than others, until the grifters take over and buy them out. JS owns part of Poloniex(correct me if it was another exchange I forget) and used his leverage to compel other exchanges into powering up users funds. The precedent is set, this will happen again and again going forward as there was not very much blow back. The only way I see around this is to invalidate powering up of specified exchange accounts, of which the witnesses would routinely update the list of official accounts. It would be a different kind of Hive account that has restrictions on it.
Decentralization requires eternal vigilance, I am confident someone will figure this out but that is my suggestion anyway.
RE: How to be a 2-faced hypocrite in 3 easy steps. Also, will Bittrex do the right thing or cave?