If you leave the the trunk open and the vehicle is in Drive, there is currently no warning message on the instrument panel. Such a warning should have an option to be cancelled in those instances where the trunk is not being closed completely because of protruding cargo, etc.
Warning appears on the instrument panel showing the rear hatch open along with a chime reminder. We believe this has been in the design from day 1.
Already done, car beeps, and shows the car status app with the trunk highlighted yellow, also a text message at the bottom centre of the display telling you the trunk is open and to proceed with caution.