I don't see any reason why BCX should attack Poloniex. The Poloniex attack might have been a smart move by the Monero team. In this way, they can scare BCX, any law intervention would put BCX on the suspect list. He may cool down a little and give MEW more time to figure something out.

I personally conclude MEW have found a hole in their system, and are trying to buy time to implement a fix, or the worst is the hole is not fixable, and they are trying to build evidence in case of the attack and reduce BCX's incentive to launch the attack.