I've been tinkering and playing with the idea for ages also but have been busy on prontoTunes lately.

I was thining if it was dynamically built (eg via code) then would the z-order be an issue? I assume (and that's always a bad thing) that if you create it, it would be at the front... Then on action you just delete it. Then just store your backgrounds corners, headers, buttons etc on a template page. Given we can now get text widths creating the size shouldn't be too hard with a parameter of how much padding on either side.

While on the whole z-order I'd love to see the ability of grouped objects, even if managed like in flash where you create a parent and then put your other objects inside it.. But only need to manage/move the first one to keep everything together.