I'm also came with the same conclusion but I can't seem to put my finger into it if Xenahort will finally be removed after this next game or will there be another surprise to keep him on it.
If Nomura says it's the finale of the Xehanort saga, I believe it is. In fact, KH3D already shows you why he may be on his last game on KH3. If you need me to spoil the beans:
In KH3D, the thirteen vessels of darkness will actually be.... Xehanorts. YES, you heard it right. They're the actual ORGANIZATION XIII. Xemnas planned the ORGANIZATION XIII as a way to open the Kingdom Hearts (like his predecessor, Xehanort). What they didn't know was that they were all going to be turned into Xehanorts. Since Xehanort himself is as dark as the darkness, he would be perfect to balance the lights. But you know what happened: some members of the original ORG 13 didn't follow with the plan so there was a revolution. The lights are the Seven Guardians of Light. In KH 1, Maleficent almost succeeded that goal by kidnapping the 7 Princesses of Hearts. 6 of them were from Disney and 1 of them was Kairi.
Oh and if you need some revelation, here are (so far) the revealed members of the REAL ORG XIII from KH3D: Master Xehanort, Ansem, Xemnas, Young Xehanort, Xigbar, Saix... and the rest are still in hoods.
Now, it might make you wonder: how the hell are Master Xehanort, Xemnas, Ansem, and Young Xehanort meeting each other? KH3D actually interconnects with all the KH games because in KH1, when Xehanort turned to darkness and made the worlds go ballistic all of a sudden, Xehanort turned into Ansem and he somehow had the power to travel through time. Through this, he met the Young Xehanort in Destiny Islands years ago before Birth by Sleep;s story happened and he told him of his plan. He probably then met all the other "members" of Organization XIII and decided that to make this plan work, they had to go through the Dream Worlds. The Dream Worlds are made up of worlds that are still in sleep and haven't been restored since Sora's victory back in KH2. But these Dream Worlds don't have the effect of time so anybody can look younger or older depending on how the worlds were consumed with darkness.
Then they had to make their plan. They only had 12 members of the ORG XIII and they chose Sora as their 13th member. But as you know, Sora was rescued before he would become the 13th member. Now, all members of Org XIII disappeared since when Ansem and Xemnas were defeated, the real Xehanort would return to his true form.
Ah yes, I forgot: when a Heartless and Nobody is defeated, the original body will return. When somebody becomes a Heartless, they leave the "shell" or body they once inhabited and it lives on its own, becoming a Nobody. But when the Heartless is killed and the Nobody is killed, the original body is restored. So imagine the glory when the favorite members of Org XIII were killed.... YES, the members become human again. So if you liked Axel.... hehehehe, he comes back again but now as Lea, his true human form.
So Xehanort will be back. But how he intends to get the members of the true Org XIII is anybody's guess.
Also, consider this doods: in Birth by Sleep, Master Xehanort (the bald, old guy) possessed the body of Terra in BBS. So technically speaking, when Xehanort comes back after his Heartless and Nobody is killed, the Xehanort we will see is the Xehanort we never got to see from KH1 since we only met his Heartless, Ansem. We will call him Terra-nort so we have a clear understanding it is still Terra but with the mind and personality of Xehanort.
Oh and if you're wondering: why would Nobodies like Xigbar and Saix be turned into Xehanorts, when they don't have hearts? Aren't Nobodies just empty vessels?
That's where KH3D proved everybody wrong.
SPOILER
Nobodies HAVE hearts. Xemnas lied about Nobodies just being empty vessels. Actually, Nobodies develop hearts themselves. The special Nobodies, specifically. They do have emotions, dreams, feelings like humans... since their hearts were darkned and turned into Heartless, the vessels left will become their own selves and in time, they begin to develop hearts. That's why the Nobodies like Namine, the ORG XIII and Roxas were like humans; they WERE humans. It's only that their original selves were Heartless. So to compensate for the lack of a heart, they made their own slowly. That's all the members of the original ORG XIII had personalities. They had hearts developing already.
There, now you know some details of the old KH gamnes and what may happen in KH3. This is going to be good ;-D