Hi ,
just one idea , why not have two UU for each civ , ... ? one early and one later game UU , ....
a lot depends on what your settings are , if you can give two or three promotions to a UU like the cho ko nu can make the chinese UU beat up the mongolians when they come , ....
for example as second uu , japan could have zero fighters , ....
france could get the FFL , French Foreign Legion as a second UU , ....
Have a nice day