Just got this slide from a confidential Circle presentation. It does more to explain Circle's acquisition of Poloniex than anything I have seen today. 
Takeaway: the SEC did indeed informally indicate to Circle that regulators would "not pursue any enforcement action for prior activity" at Poloniex as long as Circle cleans up Poloniex and turns it into a regulated exchange.
The SEC seems to be saying here that it's okay if you broke the rules, as long as you get acquired by a legitimate player before we crack down on you.
The question now seems to be whether the SEC will apply this same thinking to other virtual currency exchanges if they are acquired by large players.
