There’s a more direct version of that, I guess from KDE, called KdirStat.

I hadn’t heard of the one in the op. But if I had to guess, it looks like it’s a different take on the same idea.

I don’t have any better tips for getting involved, but I just want to say thanks! OSS clearly needs help from skilled designers all over the place. Any time someone like you steps up, it’s a good thing. n_n