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It is not even confirmed that Ventus actually lived in/hails from the age of fairytales, you're jumping to conclusions here. The only thing we know is that Ventus will be involved and that he has a connection to the era somehow. Maleficent is also involved and we know that she is the present-day one who somehow managed to get into the Unchained X-world.
Another thing to keep in mind is that Unchained X may actually be a sleeping/dream world which means not being actually the age of fairytales.
Browser-chi is most likely the one to portray the actual historical events of the age of fairytales, ending with the destructive Keyblade War, and neither Ventus nor Maleficent appear in that one.
I feel like pointing out that even if Ventus appears in Unchained it doesn't mean Ventus appears in Unchained. By that I mean Ven is in the book of prophecies, all our heroes are that's how cards and medals with their pictures were made. It could just be a hologram of Ventus, I mean that's the beauty of all this it doesn't need to be the real Ventus. It could a hologram Ventus, it could a dream Ventus, it could be a physical manifestation of Ven's dreams ala Neku/Shiki, it could be the real Ventus, it could even be some lost fragment of Ventus that split off when Ventus shattered his own heart. There are way too many factors right now to be able to tell.