Being forced to disable withdrawal and/or to take loan already kind of working as a consequence in my opinion. Is that severe enough to achieve better governance? I don't know.
That aside, a way more interesting "topic" is up for discussion now. Let's see where it develops.
Even that would only ever happen if they burned through their liquid slice and didn't replenish it fast enough from the initial power down installments, which is actually quite unlikely.
It is possible to get this information historically from the Steem blockchain since most of the exchange balances are public. For the most part they have only ever increased, meaning there would never have been a liquidity shortage with even a tiny liquid portion.
Is there any other known exchange currently voting for witnesses on Steem aside from @blocktrades?
I don't think so but I'm not 100% sure. In my opinion, mostly they ignore it because the value is low (and we're lucky when they keep their wallet updated and online), but now that they all have people whose job it is to figure out how to earn income with customer deposits, a rise in value would change the situation.