@heromed Hi!
No offense taken regarding the current design tool. I strongly agree that it is not very user friendly... 
The initial plan was to introduce a simple designer, which would then gradually "grow" into a more capable, user friendly graphical editor.
But, maintaining the GUI-O app (and basically everything else related to GUI-O), I never got this far. It is not a simple project anyhow.
To answer your questions:
It is definitely worthwhile from GUI-O perspective as it would surely be a significantly more friendly tool to create layouts. From my point of view, I see no problem if you license the editor as a FreeWare.
I only see one problem if you go ahead with this - almost all widgets are custom (low-level paint operations), which means all the logic is implemented in the GUI-O. So in order to create an editor that will be 1:1 compatible with GUI-O, you would need to re-implement the widgets exactly... Ideally, the codebase for the widgets should be the same (e.g., shared between the GUI-O app and the editor).
I am sure you understand I cannot share the source code for this as this is one of the main features of GUI-O.
Can you share a brief overview on how would you implement the editor? So we can discuss this further. 
P.S.: Which app did you develop? Can I download it from Google Play Store?
Best regards,
Kl3m3n