Somehting that just popped into my mind (abit similar to something i proposed before)
Each true neutral (even after turning pro-some camp) that gets attacked gets 1d6 extra inf (partisans).
So you can get 1 up to 6 extra inf per country, not knowing which neutral will fight back fiercely and which one will give in easily.
As they are civilians, these are ONLY for defence, when a turned neutral gets activated, only the amount of soldiers indicated on the board get drafted.
It can be called “neutral partisans”
Edit: …i guess this means if for example Russia attacks Turkey (Stalin wanting kebab) and all the other neutrals (blocks or not) turn pro-axis, the axis can chose NOT to activate Spain, forfeiting the 2 IPC income but gambling to have up to 6 INF extra in case it gets attacked. Might be interesting in certain cases.