Built in testing is easy. Noxid just has to grab the System's runtime and try to execute the Doukutsu.exe file within it. I don't know why CaveEditor doesn't have this feature, because it's equally as easy in C++.
I'm not sure what you mean by friendlier interface. Personally I find the interface to be sleek and easy to use. Sue's probably had the best interface of any editor, but not many features. CE had lots of features, but a crappier interface. BL is better than CE interface-wise. Also, do you know how hard it is to make a nice looking GUI using Java Swing? You have to give Noxid some props, not tell him to improve interfaces.