I doubt if the SEC has jurisdiction. Crypto exchanges are kind of outside the law to some degree. But if I had 10X the holdings I had on Polo and watched half the value of it vanish overnight simply because of their action, I'll admit I'd be tempted to call a lawyer. Seems to me civil lawsuits could be brought to bear if nothing else.
But I don't mean to sound overly harsh or presumptuous. Hopefully Polo is not engaged in insider trading. And there is some truth to "all the exchanges are doing it" with regards to opaque, non-transparent listings and delistings of coins. But that doesn't make it any less rotten, and it could all be done much better and more transparently. But the exchanges need to feel pressure to make these steps.
That's why I pulled 90% of my funds from Polo today, and the remainder will follow shortly. (If Piggy comes back, I expect to follow, but without it I have no reason to stay on Polo.)
A number of the coins I'm trading with are only listed on Polo, I'll keep trading for now - but if they are delisted in the future it leaves nowhere to go other than trying to find alternative exchanges which raises questions about if I should still be trading with these coins...