As per FINRA-5310.08, we as retail shareholders have the right to route our trades as we see fit—and IEX is the routing system retail shareholders would like for Fidelity Investments to enable.

FIRNA-5310.08 - Customer Instructions Regarding Order Handling. If a member receives an unsolicited instruction from a customer to route that customer's order to a particular market for execution, the member is not required to make a best execution determination beyond the customer's specific instruction. Members are, however, still required to process that customer's order promptly and in accordance with the terms of the order. Where a customer has directed that an order be routed to another specific broker-dealer that is also a FINRA member, the receiving broker-dealer to which the order was directed would be required to meet the requirements of Rule 5310 with respect to its handling of the order.