I use Chrome DevTools a lot when developing ClojureScript web applications.
Chrome/Blink developers have been pretty open for adding extension points into their DevTools.
In December 2015 I had an idea of integrating cljs-devtools with Figwheel's REPL console. But this was not the first attempt to bring ClojureScript REPL functionality into Chrome DevTools. Actually Suprematic have implemented their ClojureScript REPL extension in 2014.
I tried to request a new extension point which would potentially allow me to implement REPL functionality in a similar way how custom formatters are implemented. Unfortunately existing DevTools extension APIs had not been suitable for what I wanted to do. There had been some progress made on that issue but after six months of waiting I decided to fork the DevTools.
I don't have an ambition to merge this project upstream into official DevTools. Dirac changes are too specific for ClojureScript (and mostly implemented in ClojureScript). Instead, the idea is to maintain a set of patches rolling on top of official DevTools branch (and to maintain a battery of tests to make sure that the Dirac code does not break).
I also provide a Chrome Extension which wraps Dirac DevTools to make life a bit easier for Dirac users. After initial setup, the experience should be very similar to integrated DevTools - you just use a different keyboard shortcut to open it.
I view Dirac as an experimental ground where new DevTools features can be implemented in more relaxed way. Not only for ClojureScript but maybe for other compile-to-js languages as well. It could serve as a proof-of-concept implementation of some features requested in the official DevTools.
In future, it might be eventually possible to implement some Dirac features directly in the DevTools. But until then I decided to maintain a live fork so we don't have to beg Chrome developers to add ClojureScript-related features into official DevTools for us.