Serbians yes please. If cleverly done, they can double as troops for the 1912/13 Balkans Wars to Spanish Civil War troops up to WW2. With a headswap, could perhaps double as Romanians?

Austrian cavalry for 1914/15 would be interesting as well.

Ottoman troops should add to the existing ones, so maybe a new set of infantry wearing keffiyeh on their heads.

Great topic Marco!
I support all your requests!