Please try Viewnior before making comments. It's better than GPicView in many ways.
It has all the feature GPicView has and is as fast. It's GTK+ 3 ready, too.
Though I don't like to drop my own program and use others', I see no reason not to use it because it's indeed superior than mine. Even better, it's desktop independent.

Please give it a try and give me some feedback.
Developing another one with XFCE devs is not needed. I see no reason to do so.
Viewnior is good enough for this. If it's not, I'm sure that several patches will be enough.