After replaying Terra's scenario in BBS, I think I know what Xehanort wants.
He wants to recreate the Keyblade War in order to summon the Xblade, and with it, have access to Kingdom Hearts. But since KH is in the Realm of Darkness, then that would mean erasing the division between both realms: the wall between light and dark. He says something along the same lines to Terra.
My theory is that Master Xehanort wants to completely eradicate the division between light and darkness and have them coexist with one another wihtout the needs of a restraint on the darknes. But he wants an absolute destruction of that division. And to do so, he needs Kingdom Hearts because, that way, every single division, from the hearts of men and worlds, can be erased. Basically reshaping the laws of life as we know it.
And on the subject of Kingdom Hearts, he would need every single heart to not have that division, and let it stay that way, meaning that he will become the ultimate overseer of the universe: he will plant himself into every single heart in order to watch that said division will never be created again.
He wants to recreate the Keyblade War in order to summon the Xblade, and with it, have access to Kingdom Hearts. But since KH is in the Realm of Darkness, then that would mean erasing the division between both realms: the wall between light and dark. He says something along the same lines to Terra.
My theory is that Master Xehanort wants to completely eradicate the division between light and darkness and have them coexist with one another wihtout the needs of a restraint on the darknes. But he wants an absolute destruction of that division. And to do so, he needs Kingdom Hearts because, that way, every single division, from the hearts of men and worlds, can be erased. Basically reshaping the laws of life as we know it.
And on the subject of Kingdom Hearts, he would need every single heart to not have that division, and let it stay that way, meaning that he will become the ultimate overseer of the universe: he will plant himself into every single heart in order to watch that said division will never be created again.