Unlike some versions of Atheanthroposialism, Restitutionalism accepts that God has intended to become a man. The question is, was that intention based on his knowledge of man's defection?
Restitutionalism says yes.
"Had sin not existed, incarnation would not have been."
Thomas Aquinas, Summa Theologie 3:1:3, c.1274 CE.
Elevationalism says no.
"[That God became man] shows that we were created for this, and reveals God's all-good purpose for us before the ages, which, not admitting any innovation in its own inner principle [logos], came to fulfillment through the introduction of another, newer occasion [topos]."
Maximos the Confessor, Ambigua, c.640 CE.
As regards the original aim of the theanthroposis, Restitutionalism sees it as remedial (i.e. restitutional), to restore man to a former state, while Elevationalism sees it as elevational, to raise man to a higher state, its remedial aim being supplementary.
Restitutionalism is also known as "Hamartiocentrism" (Greek hamartia "going wrong"), and Elevationalism as "Christocentrism".
"Supplementary", not "unimportant". Indeed, the New Testament focusses mainly on the supplementary aim, and some of those who testified to the anthroposis may not even have been aware of its prior aim. But this is no evidence for Restitutionalism; to those aware of having gone wrong, getting back on track is the urgent matter, but once back on the track they must turn their minds to thinking about where it leads.
Restitutionalism can be expressed by saying that Theanthroposis was not in God's Plan A (to have been applied if man had taken the straight route to fulfillment), only in his Plan B (which applies as a result of man's defection).
This prompts the question of whether saved man's final condition will be better, worse or equal-but-different compared with what it would have been if he had never defected. Each of the three possible answers leads, via supplementary questions, to unpalatable conclusions. I know not how much support each answer has, but the usual tactic seems to be to make excuses for not answering.
For instance, Aquinas' main answer is "better":
"There is no reason why human nature should not have been raised to something greater after sin. For God allows evils to happen in order to bring a greater good therefrom; hence it is written [Romans 5:20]: Where sin abounded, grace did more abound. Hence, too, in the blessing of the paschal candle, we say: O happy fault that merited such and so great a Redeemer!"
Thomas Aquinas, Summa Theologie 3:1:3, c.1274 CE. His first quotation is from Romans 5:20, and "happy fault" is the felix culpa discussed in the Creed part of this site.
However, he keeps one foot in the equal-but-different camp; to the words quoted at the top of this page he adds:
"And yet the power of God is not limited to this; even had sin not been, God could have become incarnate."
The belief that the anthroposis as inextricably bound up with man's defection must, logically, lead to either Atheanthroposialism or Lapsofatalism. Aquinas explicitly chooses Atheanthroposialism, but when he says that God "allows" defection he probably means, not that God opportunistically seized the opportunity provided by man's impending defection, but that God had decreed that defection, which implies Lapsofatalism. As Jacques Derrida would say, he declares Atheanthroposialism but describes Lapsofatalism. However, I cite him here in terms of his stated view.
Aquinas frames the question in terms of "nature" and "grace", but for present purposes "nature" corresponds to cultural madate and "grace" to elevation, so his Scholasticism need not trouble us, and the quotations I have chosen do not rely on it.
Maximos is the earliest proponent of Elevationalism I have found.
There may be something relevant in earlier authors like Irenaeus, but I think none of them was clear on the point.
Maximos never explicitly poses the hypothetical question, but this casts no doubt on his Elevationalism; hypotheticals come more naturally to us Latins than to Greeks like Maximos (and the authors of the New Testament). He expresses himself in the distiction between logos and topos, which is clear enough given his usual use of these terms.
Duns Scotus is known as the father of Latin Elevationalism (which is accordingly known as the "Franciscan Thesis"), but he was preceded by Rupert of Deutz. As far as I know, Rupert was the first to give a clearly affirmative answer to the explicit hypothetical.
"It would be absurd to hold that he who is the head and king of all of the elect, both angels and men, would not have been born unless there had been sin."
Rupert of Deutz, De Gloria et Honore Filii Hominis Book 13, c.1187 CE.
I am not aware of any Christianoid group that positively affirms Elevationalism. It seems to have some "Eastern Orthodox" support, and apparently Josef Ratzinger (aka Benedict 16 of Rome) favoured it informally at least, but its importance seems to have gone unnoticed.
Back to Atheanthroposialism.