Just as you would expect a rapid development engine to have a good gui system, you would expect an engine geared at non coders to not have to code.
Nobody wants an html element floating over their content, and nobody wants to dig through the web to style it since there no documentation on the vast majority of possible css functions.
Did I mention the non coder thing?
I would rather try to hack something together from the mismash of parts than have to deal with a box with a z I can't control, and a refresh rate that makes it look like you are using Windows Xp.
Edit:
If you need to hand that off to a third party then fine.
Offer a subscription for an good implementation.
Do a GUI Jam, get creative.