The largest brick wall and aggressive South American player bumps into is the American Guarantee on everything. While I understand its meant to simulate the Monroe Doctrine and prevent the US from sitting idle if the Axis do attack SA for some reason, I'm not entirely convinced that the guarantees should be there.
The US did get involved all the time in central american wars. The SU took the Monroe Doctrine and bascially said that anything going on in this hemispehre is subject to US intervention. While I agree that a single war between two South American coutnries would not have resulted in US intervention I guarantee the US would have gone nuts if one country started to gobble up two, three or more other countries down there. Especially if they thought they had Axis leanings.
Sounds like your not going to enjoy the partisans feature of FTM then. Personally I think it would add a little flavor, and it could be simply added as an increase in revolt risk in some areas or under some conditions. It wouldn't be any different than the current rebels system that exists now. And if the Rebels held out long enough they would get the country, which is all ready in the game.
FTM is an open question. I already voiced concerns about more 'whack-a-mole' type stuff. But PI says it won't be like that. Some of the issues aren't units but province related. And the other improvement is not a single militia unit popping up but a coordinated (from your enemy) effort with multiple units.
BTW - this very aspect of FTM further reinforces that it wasn't the small countries doing it but the majors directing the conflict using the resources and troops of the small countries. So that Haiti Costa Rica war wouldn't happen but UK sponsered militia units appearing in Norway would. Big difference.