…Regulators appreciate that buying and selling big blocks of shares comes with a risk of nimbler rivals sniffing out trades. “It’s quite clear that the caps are going to kill off dark trading in a lot of stocks, but we might see systematic internalizers and other ad hoc ways of trading starting to flourish,” said Niki Beattie, a consultant who runs Market Structure Partners in London. “The world is evolving into something different, and we do not know what it is.”