The Imperial Japanese Army is the easiest; The Uniforms is already there - Royal Marines coat retextured with simplified cuffs and voila, M1886 Uniform if Dark Blue, M1902 if Khaki. Stick a Brass Star to recolored boshin officer hat, french marine hat, and shogunate denshutai hat and you're done. Modify Royal Marines Officer Tunic into Imperial Cavalry Atilla-style Jacket with froggings. Get Maxim Guns and German Artillery from TGW Mod. What left is just Sheepskin Jerkins Vest, Murata Rifle, Arisaka Rifle, and the humble Shovel.
The Qing Empire Modernized Beiyang Army is pretty much like that too - just grey (try watch 1911) but also need Heads with Manchurian Queue-style Hair. The Provincial Army will need much more than that though, lots of unique Chinese uniforms...
Imperial Russian Army is the harder part...TGW cooperation is most definitely needed for that...Need Beaumont Rifle, Peaked Cap, Cossack Fur Coat, Ushanka Fur Hat, Tall Cossack Fur Hat, Double-Breasted Greatcoats with Epaulettes, and Gymnastiorka Shirt with big Epaulettes. Also Madsen LMG and somehow, animation for that.
Well, haven't mentioned people would ask for Boxer Rebellion, and then the nagging for German, Austrian, Italian, British, and US Marines...
But blah, the problem is the Naval Aspect - No one made Turreted Ship Models. Ever. In a TW Game - So there sinks my dreams of seeing Mikasa exchanging fire with Tsarevich in the Yellow Sea...