It is mostly done! Lauren decided to release a preliminary version of WrathEd to compile maps. It's features are a bit limited but still very useful (especially to improve loading times and lag on custom maps).
There are however three downsides:

- As Kane's Wrath doesn't support a map stream for custom maps directly you have to do some additional work (a tutorial is in the link below)
- You have to have all terrain textures converted to dds (also in the link below)
- Maps get pretty big as dds compression isn't implemented yet so it saves the terrain texture atlas as A8R8G8B8. (resulting in ~30MB per map)

ModDB Profile 
Download 
Tutorial 
See "WrathEd/Games/Kane's Wrath" folder for available assets.

Mission maps are now fully possible in KW. I made a small video demonstrating mission objectives and weather effects:

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