I only skimmed the article (I am no cloud scientist), but I feel like vertex color skyboxes should probably be mentioned. Used in the Homeworld games and the early Spyro games.

Explanation.

Spyro example, 2 (you may need to open this in a private window for it to load properly). Gallery. (also these will likely look more natural in-game, then again they may be obscured by the map itself)

The relevant bit here is that the artist can control how soft the edge of a cloud is using the density of the mesh. Defined clouds, wisps, overcast/fog looks etc. Also, aesthetic.