Going through the list of available aircraft for various squadrons in WOFF, the biggest gaps that need to be filled, IMHO, are the following: Farman F.40
(used by several French squads mid 1916 to mid 1917). Salmson 2a
(used by both French and Americans early 1918 on).Armstrong Whitworth FK8
(British 2-seater used in several squads mid 1917 on).
It would be nice if someone could find models for these planes. If we get models, we can create FM's for them, too.
I haven't looked at the German's yet, although I'm sure there are several missing types there, as well.