Theandrosis
The world's ripeness is necessary for its union with God, but is not sufficient, for it could never be enuf to bridge the gulf between the world and God; between creatures and their creator. How can that gulf be bridged?
The answer is that men, the stewards of the world, are more than creatures, though not less. This is why it is possible for a man to be God, and a man who is God is himself that bridge. And so the world can be fulfilled.
"It is because man fundamentally reflects the personal character of God that God himself can take on flesh and blood."
Nigel M. de S. Cameron, Complete in Christ (1989). (Page 27?)
And if the fount of all goodness can do this, it would be perverse not to assume that he will do it.
We conclude that God has always intended to bring the world to union with himself by becoming a man, living as a man in the world.
In Trinitarian terms we say that God the Provider made man on the model of God the Mediator and intended the latter to achieve the union.
On technical words relevant to this topic, see here....
On the destiny of any inhuman selves, see here....
Objections
You keep saying "a man", but it could equally be a woman, for women are also more than creatures.
For God to be human is ipso facto to be male. God cannot become a woman because women are feminine. In the beginning God was masculine, and in the fulfillment he is male.
Most discussion of God becoming a man has (in English at least) focussed on his becoming a human; the sex of that human has usually been overlooked, maybe because of the confusing ambiguity of words like the English word "man". We might call it a Bull-Elephant in the Room! On 2024-08-20, a Google search for "Cur Deus Homo" (the title of Anselm's famous book written around 1088 CE, Latin for "Why God human") brings ample results, but "Cur Deus Vir" ("Why God man") has just 2 English-language Google hits.
"It is absurd to imagine God becoming a human. It is like confusing an author with a character in his story."
The author-story analogy has limitations. There is no exact analogy for God's relationship with the world. I see no grounds for preconceptions on this point, and I see no plausible alternative account of man's destiny.
(Restitutionalism) "You imply that this would have occurred even if Humanity had always done right, but the Bible tells us that it was only because Humanity did wrong."
It is true that the understanding of recapitulation arose in close connection with the recognition of Christ as saviour, but it was always in principle independent of it. The Christ-event reveals creation as much as salvation, and the Christian doctrine of creation has always differed from other doctrines of creation. That Christ entered the world "for our salvation" need not imply that he would have stayed away if we needed no salvation, and the New Covenant Book indicates that his mission to save was an adjunct to his original mission to fulfill.
"If there is a sentient body there is also a spiritual body. ... The first man Adam became a sentient being; the last Adam became a life-giving spirit. But it is not spirit that is first but sentience. ... As we have borne the image of the dusty man, we shall also bear the image of the heavenly man."
Paul of Tarsus, First Epistle to the Corinthians 15:44-49 (c.55 CE)
"And that a higher gift than grace should flesh and blood refine:
God's presence and his very self, and essence all-divine."
John Henry Newman, The Dream of Gerontius (1865)