I would recommend apropiate soviet terretories!
Briansk, Wiasma,Orel w. Victory points as well as Lenningrad,Stalingrad,Karkov,Smolensk and Kiev.
-Stalingrad ,Briansk and Orel should have more lucrative IPC’s to attrac axis player
-Stalingrad should have a harbor for the black sea
-Turkey as neutral should go to axis after you cross or gain the crimera terretory and switch back to russia if they regain the crimera, anyhow turkeys buisness should be that, that they open the bospurus for their ally who owns the crimera at that time!….
this will not result in an additional player, more likley as a automatic or tech.
such a tech could also apply for Italy/southern Italy and France/Normandy france where the nation switch to the opposing side…
just a thought