If Russia was added but not Belgium I would personally find the nearest brick and beat a random homeless guy with it. Russia quit halfway through the war because of the Bolshevik revolution - but the country who gave the allies an advantage in the war and fought from start to finish gets nothing? That wouldn't make sense.
While personally I would want Belgium in the game, I'm 99% sure that after they add the UK they'll add Austria so that it represents both sides equally - that being said, if they add a 5th faction, it should be Belgium >.>
There's no clue that Belgium must have a Nation in this mod and not Russia if you go on this way. because without millions of russians mobilizing millions of Austro Germans to face them, that's not the 110 000 belgian soldiers which could have saved us. IF we were not totaly outnumbered and spanked in 1914 it's because of the russians.
+ you forget to remember that, alot of Russian offensives like Brussilov were made by the non stop pressure and asking for of the French and British commanders to help us in great battles, like Verdun, to depressurize our front.
About the advantage you gave, Serbia gaves a greater advantage and defeated in outnumber and without many artillery and ammunitions the austrian army, starting to invade them on their own territory and forcing two times the Austrians to retreat totaly from Serbia. That forced germans to send many men to help Austrians in 1915. With they couldn't have a nation plot too so?
Only thing to make everybody happy will be to keep the last two plots for multi nations, like "Eastern Entente" with Serbian, romanian, italian (even if its not an eastern country), russian troops. And eastern Triplice with Ottomans and Bulgarians and Austria Hungary. I know this is not the best way to have a full nation units but it's the only way to make most of the people alright with that i think.