I wouldn't be a bad idea to make a mod of C&C3, that way all you would have to do is mod the whole game to your specifications. Assuming you use my idea, because it is a mod, you could do whatever you want to do with it. For example, you could take some of the characters, skins, and units of KW, put them in your mod and use them in your new campaign.
As far as campaign/map ideas themselves, you could try having a three-way skirmish in one...
What do you want your campaign to say? C&C3 and KW had quite a complicated story line. To make a campaign, I personally think one should come up with a story line along with maps, skins, units etc. I am just making a suggestion.
Controversial statements are the ones that utimately need to be discussed.