As far as I know fog is still necessary to guarantee that everyone can play the game. Many people play FH2 with weak computers (like I do currently) and removing fog would make the game unplayable to them. Furthermore, even average computers might struggle with complete fog removal on some maps. To me it's only an issue when flying to be honest, but you have to deal with it.
You will have less fog on Africa maps I think, because they don't have much vegetation.
Gazala for example has a pretty clear sky which is why I like flying on this map. Cobra on the other hand is indeed pretty foggy, but I'm sure when they would remove fog, a huge part of the playerbase would not be able to run the map lagfree anymore. And the mod can't afford losing players just for the purpose of some players with good computers being able to play with slightly improved vision.
Anyway, if there's time it could be tested how the removal of at least some of the fog would affect different types of computers in order to potentially optimize the situation on maps like Cobra.