So, if we limit our consideration of HFT to strategies which rely primarily upon speed-based exploits (trade decisions based on the examination of current marke

So, if we limit our consideration of HFT to strategies which rely primarily upon speed-based exploits (trade decisions based on the examination of current market data w/o correlation to external data sources like, say, Twitter feeds for market "sentiment"), can we conclude from the trading stack proposed for this box that most arbitrage opportunities have been exhausted by fierce competition? If the current state of the art is measured in microseconds, how much more room is there for improvement? I understand that there's a whole world of data streams from which one might attempt to predict markets, and I am explicitly limiting my question to the genre of trading which seems to be profitable via latency reduction alone.