It would be nice if we could get different foreign units in addition to National Units, either as premium or normal progression.
Example, For Germany, Finnish Törni Detachment, French Charlemagne.
For Soviets, 2nd Warsaw Infantry Division, 1st Czechoslovak Independent Battalion.
The French Charlemagne and Polish Warsaw division may be a bit controversial but its still history and it happened. And French Charlemagne were ferocious fighters like was the Polish Warsaw Division, so it would be nice to see some representation for these kind of units. France could have units for both Germany and Allied nations, but I dont really see them getting their own faction (my opinion, its still possible like war thunder did).
Now these units could be special in few ways.
First, Premium way. They could get their unique uniforms, like their cufflink and flag (Charlemagne) and possibly some French weapons. Also they could get some boost to normal progression of troop levels and “researching” normal units.
Second, Normal “Research” way. You could have them as a separate line going from, example lvl 10 campaign unit when you reach that, you get a line to example, Charlemagne and you can choose to research them or the lvl 11 German native unit. These “research” foreign units would also have the unique stuff.