I'd like to propose the new pitch measurement being effectively being B+D. I'd measure from the bottom of the hinge of the tray table on a horizontal line to the centre of the seatback with the seat as far forwards as it goes ( i.e. not reclined).

Not a perfect measure of the amount of room a passenger will have, but it's something that should be consistently measurable and doesn't rely on there being or not being contents in the seatback. At least it can give a "pitch index" as a useful comparison.