The way it is now, Soviet players aren't really encouraged to preserve your old units after you upgrade them. What if your old units also can get these bonuses, but a little bit different?
I see (at least) two options, and I'll use conscripts as an example
1. Through vet the old units can get the upgrades for free.
-Conscripts can get 8 rifles in vet 1, get molotov in vet 2, and NKVD in vet 3
2. You can buy the upgrades individually for any of the old units to make them as good as the new ones.
-Old conscripts buys an upgrade (like grens buy schrecks/Mg42 or sharpshooter buys artillery) to give them the NKVD, rifles and molotov cocktail.
I don't know how this will work with the changes in the 1.20 patch, i'm just giving ideas of improvements for how the mod is now.
Do anyone else have another solution?