I just tried editing a section using Edit source. Then wanted to edit the section using the VisualEditor, so I clicked on Edit. Only the section and references were visible. I was thinking this was a nice addition that limited visual editing to that section. Instead, after saving, the rest of the article was gone, saving only the section I was editing.

If VisualEditor can only edit the entire page, then when switching from editing a section in source to editing with the VisualEditor, it needs to pull up the entire page and merge changes from the current section before displaying and allowing visual editing. The alternative (preferred by me, anyway) would be to visually edit only that section. Section editing improves performance and limits opportunity to mistakenly change other parts of the page.