Mighty Jim said:
either way, I expect each pack to have a new set and symbol for the encounters, but to mix with core set symbols to form new encounter deck combinations.
That´s exactly the way is going to be.
As for the campaign game, reading that the six quests follow a narrative (hunting for Gollum and finnally taking him prisoner and escorting him) I expect something similar to the nightmare version of the core set to be able to play all six quests in a row with same group. Not sure if they will add any special rule for this, but would be very nice if they do. Since we will have more heroes of each sphere to choose from, maybe the possibility of bringing replacements for your defeated heroes from the same sphere for next quests?