If you're interested in market fragmentation, having a look at the fragmentation tools by Fidessa can be very useful (if you haven't already). Originally triggered by MiFiD and RegNMS, Fidessa launched the Fidessa Fragmentation Index (FFI). The FFI provides a simple measure of how different stocks are fragmented across primary markets and alternative venues. The Fragulator provides more insight in how a product is fragmented. There is even a "live" version which is labeled Beta in google fashion.