Ok, my dream mod is a total conversion mod based on Frank Hebert's Dune.
The game would take place in Arrakis, the desert planet.
The faction/clan system of the base game would fit nicely to have all the families and cultures from the books.
One could have all the troops like different Fremen warriors, elite Sardaukars, Atreides soldiers etc.
The combat system would fit perfectly to include melee sword fights, ranged blaster fights and shields converted to Holtzman Shields.
One could also try to switch the mounted cavalry of the base game to the hovercrafts and ornicopters etc. (i dont know if that would work lol)
During the campaign map gameplay, the characters would be mounted on the above-mentioned flying engines, navigating the dunes of Arrakis.
I would personally choose the timeline of the book 'Children of Dune' so that some parts of the planet had ungerdone the climate change, blossoming with green flora near the water.
Imagine all the city scenes of Fremen underground caverns, regular Fremen orgies, newly formed surface cities etc.
Chilling in a damp Fremen tavern with your blue eyed lads, smoking up melange would a a memorable event for sure.
One could create melange mines on the campaign map which would be like castle fiefs from the base game where one would need to lay sieges to acquire, and then they would need to create safe caravan routes to bring the melange back to the cities, which would create the much needed "Spice flow"
Melange would be the most important currency in the game, if you were low on melange your cities and troops would slowly fade into chaos, and a well melange-fed army would carry some perks with them.
Don't even get me started about the sandworm encounters that you would have to engage in around your melange mines, to protect them.
Please don't consider this post as a developer post, since I'm not even sure if all these features can be modded and are supported by our engine.
But daamn, I'd play the **** out of this.