gtk-vector-screenshot program can be used to take vector screenshots of Gtk-3 applications. It seems to work by asking the application to redraw itself onto an SVG canvas.
Emacs on GNU/Linux can be built with Gtk+, but trying to use the aforementioned application on an Emacs window results in a screenshot that only contains GUI elements such as the menu bar; buffers are not rendered (I tried with and without Cairo). This is not too surprising, given that Emacs' buffer rendering happens at a pretty low level.
Still, is there a way to take scalable vector screenshots of Emacs?