Vector Screenshots
Since we don't have up-to-date mockups of most applications, considerable effort goes into recreating existing applications in Inkscape, just to change a few small things in some cases. If we had a way to take SVG screenshots, this would drastically reduce the effort required to quickly visualize an idea, and lower the barrier to making mockups. This could be part of the system screenshot app, GTK inspector, or a stand-alone tool.