From my understanding they'll now be reflected in the NBBO, meaning if they have the best price, the order will have to be routed to them.
Ok, but if you are a retail trader and the NBBO does not involve an IEX quote, then it seems like HFT will just screw you over just like before (assuming your broker just routes to the NBBO exchange). So I guess I should hope IEX takes close to 100% market share so that HFTs go extinct.