I believe part of the problem causing GUI's-over-http to be a pain in the caboose (LimitsOfHtmlStack) to develop in is that there are too many browser variations and brands. To simplify this, there should be a single open-source code base for a GUI engine and/or "GUI browser". It would be roughly comparable to Flash.
There are still versioning problems with this, as with anything, but it would be a smaller problem than Microsoft versus Mozilla versus Google versus Apple versus Opera etc.
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