I can’t help the fact that China is a playable nation in G40.
You could if you wanted to…
USA takes direct control of unoccupied China (Szechuan, Yunnan, Hunan, Kweichow, Sikang, Tsinghai, Kansu, Shensi, Suiyuyan, Chahar, Anwhei, Hopeh.) Place USA roundels in all these territories. All Chinese units in territories with USA roundels are switched out for American units. China is considered USA supported Chinese Forces, represented by American units and behaving according to Normal rules for USA movement.
“Comintern” basically do the same thing as above except place one of those Chinese territories under the aegis of the Soviet Union. Hopei or Shensi or both, would make the most sense, given the way China is compressed on the G40 map. Instead of the Kuomintang KMT under direct Washington control, you would have these spaces as Communist Chinese CPC forces under direct Moscow control.
And if you go that route you should make Mongolia a proper Soviet puppet too.
To me part of the interest in developing a third faction to begin with would be the endgame potential where victorious factions could immediately declare war against their former friends. So on the Axis side a situation where European Axis could go to with Japan. On the Allied side, one where the Western Allies could go to war with the Soviets. And basically play on for another 20 hours lol. In that sort of situation a battle ground in China could be fun, as the United Front totally collapses and the Civil war is resumed.
Just food for thought. I’m not really the biggest fan of China as separate faction with its own weird rules.
China aside, the main thing you’d need to figure out is what sort of Victory Conditions you want to adopt, and how the two “Allied” factions (the Western Allies and the Soviets) figure into that. How do the players actually win, under this new system?
Also, pretty important too… I’d say its almost pointless to develop a game that cannot function as a two player 1v1, because most people only have a single opponent that can commit to a game like G40 with any kind of regularity. Most FFA 3 way games have a way of stalling out in fairly short order, or when one of those 3 players quits prematurely. That doesn’t mean though, that just because you have a game with 3 factions and 3 turns, that it can’t still be made for 2 players.