Wow, Uhm. You are a bag of wonders. Always something!
I think I can see where you are coming from with this idea. It could be interesting I suppose, but there is one drastic thing that seems to be overlooked, IMO, and that’s that no one really has control over their output in this sort of WYSIWYG fashion. I envision Dreamweaver’s design view of Front Page whenever someone suggests something like this. I was actually, just yesterday, walked through an AJAX driven WYSIWYG editor for a wiki application called social text which sounds a lot like what you aren’t detailing here.
The only reason I am reluctant to incorporating this into the GMS is that I don’t think that it will allow the true control that you are foreseeing while basically dumbing down the interface a bunch. Other catches that your idea faces are things like creating new PHP elements and having to have them all registered with your list, and for instance on my Drupal app with gneu, I have nearly 30 blocks of content that are all thrown around my site, and the only really simple manner of dealing with it is a drag and drop interface like Google has on its personalized home page. If anything I would rather focus on the blocks idea and allow dragging and dropping, but that too is very cumbersome as the focus of the app is not going to be slick or stylish until working, fast, easy to extend and secure are valid labels for it.
The focus for GMS is not for incorporation into a site. Building a template takes an hour and a half, plopping the appropriate PHP tags to output the appropriate information maybe takes another 30 minutes, so where is the reason for having a whole new AJAX tool that’s only purpose is to speed up the fastest part of website application development? I don’t see it as yet, and I don’t think that it will be something that we will put much energy. The Drupal drop down and weight system works perfectly fine for me. It would be very nice for eye candy and intuition I suppose but you are the first person to ever tell me that Drupal was difficult to learn.
Maybe we can incorporate this idea in as a plug in and see how much good it serves. I really have no qualms to such things and would love to give it a try. I just think its a bit much to be worrying about considering we aren't even at our 1.0 release of GMS.