The planes and artillery are so small they could be any model. The tanks are OK for everyone, as the Germans used more of these than their own version. Not bothered about the ships, so this really isn’t too much of an issue to me.
To a large extent equipment was interchangeable within each alliance; all the Allies used French planes, the US used French tanks and artillery, Russia imported American rifles.
If HBG decide there’s a market for additional units (I’d be one), then my main wishlist would be for:
A decent sized fighter plane. Different models for each side would be a bonus.
Ditto the artillery.
Bombers. By choice Gothas for the CP, Hanley-Page for the Allies.
Cavalry. Not convinced these were as obsolete as many assume. Not much use on the western front but could be important elsewhere.
Destroyers. Mainly thinking about mine laying/sweeping role.
After that it a matter of chrome;
Extra infantry types:
A basic type for each empire, the reverse of the official ones in regard to late/early war kit. That is, if the game comes with early war “pickelhaub” Germans, the additions need to be late war “stahlhelm” infantry. This distinction can be use to differentiate between raw and veteran troops, regulars and elite/stromtroopers, or the steel helmet version can be a tech upgrade.
Colonial troops:
Generic Askaris (in black). Will serve in any army.
UK: ANZACS, Indians, Arabs, South Africans?, Canadians?
F: Portuguese (UK sculpt in blue), Belgians
T: Bulgarians
R: Romanians, Serbs
G: Mexicans
A: Slav units?
I: Albanians?
Generic neutral units for house rules (Dutch/Greeks in white?)
Generic Revolutionaries (early Russians in red).
Reconnaissance planes.
Heavy artillery (howitzers).
3 extra types of fighter per side to represent tech upgrades.
Armoured trains with frickin’ lazer beams on the front.