i dont think IC will make a campaign until Sins 2, or at least until the 3 X-packs are done. they have said there will be 3 expansions, but not that it will be limited to 3 expansions.
ive been trying to think myself... atm, Sins is a great game for skirmishes and MP matches, but it is missing the flair and uniqueness of a campaign map.
unless they use the third X-pack to introduce alot of the things needed for a camaign (neutral labs to capture, ship designs to plunder, more planetary bonuses to give expansion even more importance (for instance, on a ground based RTS, you can expand to what is a secure location, or you can risk it and go that little bit further for that extra oil derrick or whatever. in Sins there isnt really this concept) and, a few other things) and, of course, they figure out how to limit the introduction of new tech to give a slow learning curve (assuming they are going that way)
its alot of work. most games are based around a campaign and story first, then altered for MP later. Sins is the other way around, so its going to be difficult
i have faith though