i think it could be like in a tabletop game where you need to conquer the whole world ( don't know its English name :/) at the start of the campaine each faction will draw some main objective cards and some more secondary objectives the winner is the faction which reaches its main objective at the end of the campaine + has more secondary objectives now we could think about what an main or sec. objective could be ^^
Most of objectives probably will be tied to ground control or strategic structures control like in most wars. I guess there will also be some more sophisticated and different secondary objectives, they could be basically anything from killing a vip xx times to finding a relic in dungeons.
Hopefully asymmetric campaign goals unique to each faction. Capturing the most territory kind of seems like it will get dull rather fast.
I second that. It also wouldn't make sense for Eldar (unless we speak of a Maiden World) and Space Marines (who aren't really supposed to hold large areas; that's the IG's job).
They did say factions will have varied objectives (think Risk). So even if they basically lose a campaign and the continent by relation they could have still succeeded in doing their personal faction objective in the current campaign. Thus they havent completely lost, the devs talked on the matter. Ill try and dig it up, though i think it was in the AMAs.
But in such a case it will be hard to determine who the winner is, unless it will not be important at all. It doesn't matter that much to me, I just wish to have a good time.