This is just a suggestion. And I think this would be a good addition to the feature of WF. Having this will let us download the PAGE only (css/html within the particular page) we're working on. Rather than downloading the whole full template zip file.
Why not just duplicate the site and delete all other pages? I doubt they would spend time on such a feature with so many more important things to work on.
That's exactly what I did and I guess you have tried that yet. I mean right after you duplicate it, it will send you the WHOLE CSS/HTML files of all your pages.