I know what everybody's thinking, "His body's been possessed by Xehanort". True, but his Lingering Will still survives. In order to travel through time, you have to discard your body, and you can only travel to where you've previously existed. The Lingering Will technically fits both of those categories as it neither has a body nor a heart.
The Lingering Will could pull an Ansem, Seeker of Darkness in which he makes his younger incarnation of himself time-displaced, essentially giving himself Young Xehanort powers to travel through time. Unlike Xehanort however, this younger Terra only travels forward in time to fulfil his duty as a Guardian of Light. Maybe Terra's conversations with Namine helps kickstart the journey for The Lingering Will to travel in time.
Having a young Terra be a Guardian of Light makes sense for one of two reasons. Firstly, as of posting this, we've yet to see Terranort. Maybe Master Xehanort no longer needs Terranort because Xemnas (who is the nobody of Terranort) is a more reliable vessel. More importantly, however, Terra deserves a true redemption arc to further develop his character. Making him the time-displaced light counterpart to Young Xehanort can help achieve that.
The Lingering Will could pull an Ansem, Seeker of Darkness in which he makes his younger incarnation of himself time-displaced, essentially giving himself Young Xehanort powers to travel through time. Unlike Xehanort however, this younger Terra only travels forward in time to fulfil his duty as a Guardian of Light. Maybe Terra's conversations with Namine helps kickstart the journey for The Lingering Will to travel in time.
Having a young Terra be a Guardian of Light makes sense for one of two reasons. Firstly, as of posting this, we've yet to see Terranort. Maybe Master Xehanort no longer needs Terranort because Xemnas (who is the nobody of Terranort) is a more reliable vessel. More importantly, however, Terra deserves a true redemption arc to further develop his character. Making him the time-displaced light counterpart to Young Xehanort can help achieve that.