Actually Praxis, you are incorrect...
A player can download a mod, then go into their Assets\Scripts\Campaigns folder and edit their race conquest.mct file and add in the missions added by the mod.. such as the Karnak EEK Missions or the Pelcian missions by continuing the pattern of the numbered mission scripts.. this will add new missions for selection into SFC 3 single player.. and if a player edits thier *.gf files in MetaAssets\ServerProfiles\Singleplayer folder, then they can use the NW Server Guide for SFC 3 or the Korah D3 guide and set up their own custom campaign parameters.. and finally if they use the Artifex map editor with the proper definitions file, they can make their own map and save it in Meta Assets folder and edit the race conquest.mct file and replace the *.mvm file with the name of the one that they made...
as such, the person would have a custom Single Player campaign based off of a mod.
Also, GAW v1.05, whch I am uploading right now has a Single Player Campaign mode that nannerslug has been working on.. hopefully the changes in the *.gf files will remove some of the bugs... Nanner will have to test it out to make sure that Single Player mode works correctly.
Hope that this helps.