Can it be a good add-on to have the capability to undock/detach "Your Answer" and the underlying preview section in a separate modal so that an answer-er can flexibly use the size of the modal to frame the answer in an full page format?
Right now, I agree we have the capability of extending the text-area height and I like it.
The idea of (at least) the preview section of the Your Answer part of the page is to give you an idea about how your answer would really look in the page.
Meaning, whatever you see in the preview, is what you get in the answer (in terms of spaces, where lines end, markdown, etc).
If you detach the "Your Answer" part into a separate "floating" module, you lose some of that (specifically the "where my line ends" one).
That's why I disagree with this feature request.
