I would guess one of two things. 1). The tower is about to burn. All former tower activities will be relocated to the reef. 2). All level 32+ activities are going to be relocated to the reef. There will be a new cryptarch. Their will be a new vanguard QM, with a new rep grind. Like: Elite Vanguard QM, starting a faction level zero. Similar with all other factions. Or the vanguard QM won't have anything new, but their will be a new, separate marks vendors for vanguard and crucible marks once you've ranked them up. New bounties since you won't need to grind the old bounties anymore.