Versions of both of these exist in the FX market ("last look" and "latency floor" if you want to Google). They are successful in reducing, but not eliminating,

Versions of both of these exist in the FX market ("last look" and "latency floor" if you want to Google). They are successful in reducing, but not eliminating, the advantages of lower latency. It's not clear that they make the market more efficient or cheaper for unsophisticated users overall.