You don't happen to know what this phenomenon is called, do you? I've been looking around, and haven't managed to Google it yet.
(1) What a tall guy he is.
(2) I just realized what a tall guy he is.
That's definitely not the same thing as the question word being in front and, say, being the object of the verb...
(3) What did the dog knock over?
You can't rearrange (1) such that the "what" goes away.
(4) * He is what a tall guy.
If you were going to draw a parse tree, what would it look like? Surely a lot of ink has been spilled about it? I don't even know what it's called for sure. Something like a "wh-exclamatory statement"?