To which extend do you think market fragmentation (as a result of reg NMS) is part of the problem?

If i understand your reference to "hidden liquidity" correctly, you have simple order types and when compared to other venues.

Wouldn't it be better for price discovery, if all US equities were traded in one continuous limit order book instead of across a dozen venues, each with its own funky order types and quirks?

if you agree, i cannot help but think about this xkcd https://xkcd.com/927/