It looks as if we all agree upon the following three points:
God “plans for the future”, which is the Kingdom of God.
So I dare to continue the discussion by expanding on the preceding points:
All possible histories are contained in God’s mind and their end is God’s Kingdom, “the actual future”. God looks at all possible histories from this end.
The history without sin is in principle possible. It would have been rather weird that in such a history humans were submitted by God to illness, suffering, and death. For the same reason it seems fitting to assume that in the beginning God creates humans in a stage of original Grace (Albert Leo‘s “original blessing”) so that they were completely free to love God: The only sin they could commit was that of pride (they were not hampered by fleshly tendencies to sin).
For all possible histories where sin happens, God could have planned that those who sin are cast away without possibility to atone, and the earth is populated only by righteous people at any time.
However we know by Revelation that God loves us so much that sent His Son into the world to save the sinners. In this sense we have already concluded in previous postings that God’s suffering Love is something intrinsic to the Holy Trinity (as the paintings of the “Throne of mercy” magnificently illustrate).
This amount to say that God’s redeeming Love extends to all possible histories and all possible sins: To save the sinners God lets them on earth in a stage of “need of Redemption”, that is lacking “original Grace”.
From our perspective God’s plan of Redemption is triggered by the first sin in history. In this sense this first sin can be called “original” because it initiates the stage where humans are in need of Redemption. So what is transmitted after the first sin to each future generation is the “stage of need of Redemption” or “lack of original Grace”. God adds no “touch of sin” (no spiritual damage) to “the souls he delivers to the womb”.
From God’s perspective each sin is like the first one: it “contributes” to God’s death on the Cross.
So, in my view, the Multiverse may also be useful to approach “the mystery of the original sin”: From our perspective the original sin is the first sin in history, the sin that actualizes God’s plan of Redemption and initiates the stage of “need of Redemption”, in which humanity is till God’s Kingdom comes at the end of time.