> As it stands the 611-612 series rules pertaining to sub-penny pricing allow for average price executions; a large percentage of U.S. equities volume already t

> As it stands the 611-612 series rules pertaining to sub-penny pricing allow for average price executions; a large percentage of U.S. equities volume already trades at mid or within the spread, both principally and on venue. True, but only lit decimal penny prices are protected by NBBO. Particularly when it comes to retail flow, that gives internalization pools a license to charge high prices by only having to match penny ticks. If sub-penny was protected by NMS, then lit exchange quotes could narrow the NBBO spread, forcing the internalization pools to give retail traders much better pricing. Also in general, I suspect price discovery is much less efficient when it occurs outside of lit quotes. If not just because, there’s no transparency on book pressure. But I’m definitely less confident about that assertion, and haven’t seen it quantified in any way.