The most useful addition for me would be to set the viewport for export. Maybe simply make it the current visible window area, so it can be set by resizing the browser window?
You are talking about PNG export, right? Because with SVG you can just crop any portion of a map without quality loss. The problem is that due to implementation details of OpenFL (which is used as a drawing engine) I can't implement zooming. Eventually it will be fixed this way or another.
No, I'm talking about SVG. Right now the SVG export and the image shown in the browser have little in common. Specifically, the SVG is always portrait and includes a lot of empty space. That means editing every exported file manually.