option to take screenshots at a certain ratio

As discussed in this appstream issue, Appstream suggests taking screenshots at 16:9 ratio. Currently we must take the screenshot and then crop it to have the 16:9 ratio. It would be nice if the second step could be avoided.

gnome-shell allows to take screenshot of a selected area with the shortcut Shift+Prt Scrn. Can you add an optional setting to force this selection to a certain ratio? Default should be unset, but the user should be free to choose 16:9 or other formats in Dconf editor.