First I want to state that if you do not want a campaign, please don't simply say that you don't play them so we don't need them.

I think that a SoaSE Campaign needs to be dynamic.  In other words, each mission would often have entirely different events happen when you played it.  For instance, the first mission for TEC may have you controlling an outpost with 3 worlds when the Vasari attack.  A capital ship bombards your planet, and rather than accept the damage, you save and reload.  You prepare for attack, when suddenly an allied planet in a different star system is attacked by a large Vasari force including siege frigates.  Suddenly the game is unpredictable and unique each time.

I am NOT suggesting "destroy this base or another time destroy that base...".  Each event would be significantly different.  I have never liked "mission one, blow up the enemy base; mission two, blow up the enemy base..."  Something might happen where mission one, you destroy one of 3 very different bases, with secondary events changing the game up a bit more.  The second mission, you would have to destroy a fleet that is moving on worlds of one of several allies.  The fleet composition would change, as some of its losses would be replaced by new units each time it attacked a new planet.

SINS campaign definitely cannot be made fixed.  The game style for SINS (to me at least) is having a different game each time you play, and a campaign operating on that style would be very replayable.  However, it would need an option to allow you to fix settings for events (the events being hidden on default until you reveal them).  On the other hand, a fixed game style in SINS simply wouldn't work in my opinion, since the element of replayability is lost and you get into a set of "blow up as much as you can as fast as you can" since this game is often large-scale.

Something else that would be interesting would be rather than attacking every world the enemy controls and killing the same defenses again and again, you could find yourself in a situation where there are key worlds that must be taken, with secondary targets that supply those worlds with ships.  You would also have a chain of other hostile planets that serve no objective purpose, but simply pump out ships to attack you.

Just my thoughts on how a SINS campaign might be put together.