I'm very much intrigued by your work to use IFRAMES instead of xmlhttprequest. Is your work available for download. I'm especially interested to see what kind of polling mechanism you've used. Or are updates simply event triggered? I'd also like to see what sort of error handling you may have come up with.
This was a very interesting read, so I'm glad you and everyone else has been sharing their thoughts!
It comes with an example that script test_ajax_form.php that demonstrates how it works.
The plug-in changes the target of the form to the IFrame before submitting the form.
On the server side, the plug-in intercepts the AJAX request and posts a message in a queue of the PHP forms class object. The applications must get the messages in the queue and respond to tell the plug-in what to send to the browser as AJAX response.
Several actions may be executed, like inserting or replacing some HTML, redirect the browser to a new page, wait for a while, etc..