My most common scenario is to open an image, make some edits, then Export it to a flat PNG or JPG. Then I want to close the working image, but I rarely want to save it out as a Pixelmator doc. The dialog comes up with the Delete option, but you force me to reach for the mouse to click it. Please add Cmd+D as a keyboard shortcut.
For what it's worth,Cmd+Shift+E for Export would be nice too, but I already have a work around for adding that myself in the macOS Keyboard preferences.