I love the way gloom looks in the world, and I wish there were more effects related to the various affinities to transform areas even further!
Lets have things like necromantic corruption, or demonic corruption afflict the landscape (I know Gloom is kinda like a cross between the two wierdly enough..) but you know give me the old undead wastelands and cracked fiery hellscapes with their own unique effects.
But we dont just have to do 'bad' corruption. We could have corruption like Celestial corruption, where areas are bathed in a celestial sheen, or a more wild 'overgrowth' corruption where the plantlife has thickened immensely in an area creating a denser forest variation.
All of these could come with their own forms of attrition for invading armies and immunities for those with either the right tomes or society traits!
Umbral Disciples has such a cool mechanic with gloom and it would be a shame to only have one form of world tile corruption in existence when there are so many opportunities for more!