Some years ago, Kromm
reckoned that someday there would be a
GURPS Military. Making that capable of serving as an update book (a la
G: Transhuman Space: Changing Times) for the WWII line would seem like a good way of making more from the existing
WWII material and making it easier to write more.
There are some relevant items on the
e23 wishlist: Supporting Cast, Vehicles and Leaders PDFs, plus obvious potential for Loadouts.