Not sure if people even use this these days, but I find it to be a pretty neat feature.

Upon trying to get this to work with missionConfigFile I also happened upon a bug when calling fn_createObjectOO.sqf. The parameter check is built the wrong way around, trying to pass an ARRAY parameter with numbers - it instead detected as a SCALAR.

if ((count _this) > 1) then 
{
	_constructorParams = [_constructorParams];
	if ((typeName (_this select 1)) == (typeName [])) then 
	{
		_constructorParams = _constructorParams + (_this select 1); // This should be the array
	} 
	else 
	{
		_constructorParams = _constructorParams + [_this select 1]; // Not this
	};
};

The fix:

if ((count _this) > 1) then 
{
	_constructorParams = [_constructorParams];
	if ((typeName (_this select 1)) == (typeName [])) then 
	{
		_constructorParams = _constructorParams + [_this select 1];
	} 
	else 
	{
		_constructorParams = _constructorParams + (_this select 1);
	};
};

As for the oversight, as formerly mentioned - this does in fact work mission-side which I think is pretty neat and can help make code a wee bit more readable. As for if this method has poor performance or is susceptible to hacking - I do not know.

// Old, meant for addons
_class = configFile >> "CfgOO" >> _className;
// New, works for missions
_class = missionConfigFile >> "CfgOO" >> _className;

I understand why it was made this way, but think it'd be neat if both would work as I find iterating via a mission to be a lot faster than having to constantly close and restart Arma 3.