https://www.khinsider.com/news/-SPOILERS-Union-X-Confrontation-18081
Spoilers!
Seems as if the Heartless in their true form are invisible creatures that infest Hearts and fulfill their desires(negativity is the one they usually sense) while also fulfilling the will of the Book of Prophecies!
The Heartless are desperate to fulfill destiny yet refuse to work with people like the Master of Masters(who it calls an “old friend” like he is an old nemesis) and his Apprentices!
Once the Book of Prophecies is fulfilled what will happen I wonder…
The posts on the KHInsider thread seem to believe that the Heartless Ansem Seeker of Darkness is indeed one of the Darknesses like Vanitas is.
Of course since Darknesses are the Heartless according to Dark Road that is quite accurate! Xehanort’s Heartless is the thing that imprisoned Terra while the Heartless Ansem is most likely(judging from Xemnas’s dialogue) Ansem the Wise’s 1st Heartless(with another named DiZ taking advantage of him after Ansem Seeker of Darkness got rid of him)!
With the fall of Xehanort and his being pulled into the Light the 1st Heartless of Ansem the Wise AKA Ansem Seeker of Darkness will probably manifest on his own due to being stripped of his host!
He probably already separated from Xehanort before the 3rd Keyblade War leaving Xehanort with only the Guardian(Xehanort’s Heartless) inside him until Kingdom Hearts destroyed it turning him into a Kid again!
Since the Book of Prophecies is fulfilled the Heartless will have no reason to go around turning people into Heartless(unless ordered by Maleficent who has power to boss them around) and be easily convinced that they separate from their Hosts and become civilians. Of course that is when the Forces of Light will make their appearance!
The Heartless are in both the Realm of Light and Realm of Darkness so they technically outnumber the Light which should be enough to threaten them into action once the Heartless abandon their Hosts!
The Lights will most certainly start consuming their Hosts’ Hearts from the inside(just as the Heartless did under the instruction of the Book of Prophecies) and begin a wide scale assault on the Worlds and their peoples!