I think this is pretty much a given - session length on mobile is known to be shorter than desktop. The upside here is that we should be able to get more sessions from a user over a given time period because a users phone is with them at all times. So we should be able to compensate for length of session with number of sessions. 

Upping number of sessions is tied pretty tightly to notifications - Facebook and Twitter get people to come back to their apps by pushing notifications when something interesting happens. Pushing notifications for items in a users feed, or changes to watched/saved pages, etc could be a way to accomplish this.