I have heard from a reputable source that the second set of Scars of Mirrodin will feature Two distinct type of booster packs (ie. cards will appear in one or the other...not both). The two types of booster packs will coincide with two different "factions". My thinking is it will be "Mirrodin" and "Phyrexia". Mirrodin could be led by Elspeth and Phyrexia by Tezzeret, since there is rumor that there will be new incarnations of those planeswalkers in the Scars of Mirrodin block. My thoughts about the last set involve Karn repairing the damage from the war against the Phyrexians. (The novel aptly named "The quest for Karn")

I was also told that during the Pre-release for the second set, each player will have to choose which "faction" they wish to represent and will receive only those booster packs to build a deck. Sounds pretty interesting...I wonder how "high level" events will work.