User blog comment:ShadowSolaris7/Wolf Pack Mode?/@comment-5266147-20120719121915/@comment-1888015-20120719123855

Because it would require two different ancestors to perform the co-op from an in-universe context, which would only provide each player a proper co-op experience when they're near to each other.

Since it would only be likely that siblings, friends or lovers (in context) would be that close to do the same plan together, it could work on that regard, but it doesn't always guarantee that they'll be able to see what the other will be doing all the time.

Also, for as much as we know already, Ubisoft hasn't actually specified that two people could be placed into one genetic scenario that isn't based on the training simulation which is the Animi Training Program.