Big boys don't want the rules of this game to change. http://finance.yahoo.com/news/Flash-crash-panel-mulls-big-rb-1185462820.html?x=0
This is the right and important idea but I have been told that on the NYSE that perhaps only 80 percent in done on exchange. 12 years ago maybe 90 percent was on exchange.
http://markets.cboe.com/us/equities/market_share/ About 60% done on the lit venues - about 40% down dark.
What fraction of that 40% do you think is due internalized institutional flow? I should know that number, but I can't recall it.
Low liquidity names - a lot. Very low liquidity names - very little. High touch institutional - very very desk dependent based on their internal "relationship" and their in-house algos. My desk's U.S. listed fills are almost all done in lit venues. Changes the amount of rebate and the whole thing changes. For the longest time, our desk wouldn't allow a rebate to be reflected in our trading costs. Viewed it as a conflict. That lasted for a while the HFT came about and screwed things up. That seems to be evolving into less of a problem.