I am very late in seeing any of this thread, but there’s a sort of cheat that it looks like many people don’t know about which will likely help folks.
If the user puts an alias in ~/Library/PDF Services to a folder, volume, or application capable of accepting PDFs, then there will be a menu item in the Print dialog under the PDF submenu. Whatever the alias is named will become the name of the menu item. That’s helpful, but there are more ways of utilizing this.
Assume an alias to DEVONThink was created, and it was named Add PDF to DEVONThink. In System Preferences > Keyboard > Shortcuts, adding a shortcut under App Shortcuts > All Applications gives this user-created PDF menu item a system-wide keyboard shortcut.
Now for Keyboard Maestro. Create a macro which invokes the Print menu item, then maybe add a step for a brief pause to allow for the Print dialog to appear, then have Keyboard Maestro simulate the keyboard shortcut for Add PDF to DEVONThink.