Marked as wishlist as this could be a feature implemented for convenience. The regular shortcut to make a rectangular selection for screenshot could use an option on the notification popup to go straight to Spectacle's annotation feature, so it is no longer necessary to open Spectacle itself, select Rectangle Region, click to take screenshot, select rection, take screenshot, wait for Spectacle window to open again to then click the Annotate button. Makes Spectacle dismiss apps like Flameshot or Ksnip. It could also be implemented for fullscreen captures as well as Active Window if someone needs it.