Fog Cards
Since Recon, Spy, and Surveillance cards effectively change the fog level for parts of the map for certain players, it seems that it should be possible to make "Fog Cards", which apply fog settings to parts of maps.
This could be used to create really interesting strategies (for instance, setting Heavy Fog over a bonus you're going to attack by surprise, masking your movements and hoping to overwhelm your opponent with sheer numbers). Setting "No Fog" on part of the map, to reveal an opponent's movements to their neighbour, could also be a useful strategy. Yet another might be to use Complete Fog to hide your movements, set up some blockades, and make your getaway.
This allows some of the most interesting features of heavier-fog games without turning the entire game into a novelty exercise.
More interestingly, since cards have variable duration, users would be able to create inventive and innovative scenarios. Use a "permanent" Dense Fog card at the start of the game to designate features on the map (like bunkers and mountain ranges).
Here's a more detailed discussion on the forum:
https://www.warlight.net/Forum/107556-new-concept-fog-cards
This seems fairly realistic (the code for something like this is likely to already exist in the implementation of Recon, Surveillance, etc., cards), and would open up Warlight map and scenario design for a variety of new strategic types of warfare.