This is especially troubling. Are there any exchanges that actually have registered with the SEC? If someone like Bittrex got slammed by the SEC then it would deal a severe blow to many alts, some may never recover.
EDIT: seems like Bittrex is on top of this and compliant with SEC regs:
https://www.cryptoninjas.net/2017/07/29/bittrex-recent-sec-digital-asset-ico-investigative-report/
Being an exchange that has high volume of traders, this is good news because many traders are putting their money to this exchange and since SEC are doing something to crackdown those exchnages that are non-compliant, this would leave the traders who use this exchange a peace of mind. I use this exchange as well and knowing that they already act and do the necessary things to be compliant then I would continue to use this exchange.