I'd say IEX has done remarkably well - it's not likely to displace NASDAQ or NYSE but it has solidified its place as the #3 US exchange by any reasonable measure. If TXSE achieves comparable market share I'd call that a wild success.

You're not wrong to say that most participants don't care about what IEX offers, but enough do to make a meaningful dent in trading volume.

That’s what always surprises me when folks bring this up. Nobody in the market cares. Institutional investor experience some of the lowest trading cost in history. These complaints are most often coming from retail traders where again I don’t follow the argument. Instead of some guy on the floor picking up dollars with have machines picking up pennies. This is a win for everyone.