It's a fork from 3771a79 with some custom changes. We tend to use the GTK version as it used to be more stable than the Qt version. I am not sure if that still is the case and I know GTK will be deprecated - is it at the point now where Qt version is better maintained, i.e. from the point of view more people are generally using it these days in preference to the GTK version?
I don't mind adding in Qt if I have to but was managing fine to build just GTK previously. I guess the "Can't find Qt. It will become a problem at some point" warning is now true :-)
Robert