Was there really physical fruit on the tree of knowledge of good and evil?
I believe so . .
Was it actually the fruit itself that contained a property that would open ones eyes to good and evil?
No. There was nothing mystical or magical about the tree at all.
Adam had high intelligence prior to the fall, for he was given the responsibility to take care of all the garden and the animal kingdom. So he had knowledge. However, he revealed he was not satisfied with God's providence, but desired all that God knew and possessed. He was warned that breaking the command, and choosing to eat of the tree would cause death, but he simply did not believe it . . and because of his unbelief, he learned of death and such forbidden knowledge corrupted his being. Ecclesiastes 1:18
I've heard folks say that there was nothing special about the fruit itself (ie. it was just some regular fruit but had no such property), and that it was only the disobedience itself that was the problem, not the fruit.
Yes. I remember when my daughter was a toddler, I gave her specific instructions not to touch plug outlets, which only attracted her to them, and she immediately crawled to one and stuck her finger to it. She was not hurt, but that seems to be a common condition. Forbidden things attract us.
If there was not actually something special about the fruit, then why block access to it?
I believe it was a divine demonstration of the limits of the creature. After all, the Godhead covenanted to provide redemption through God the Son, who would be slain, before creation. A creature cannot be like God. Adam was created, and thus was fallible. There can be no such thing as a created and infallible
ousia.
If some other creature besides man ate the fruit, would their eyes have been opened to good and evil?
Only Adam, as a man, was created in the image of God, and possessed the intelligence to comprehend the moral commands of God. Brute beasts cannot reason, so they do not sin.
And angels were created only to serve God; they cannot function autonomously from God; hence a third of them were not permitted to remain in heaven because of leaving their first estate (purpose).
And what has, or is going to happen to that tree?
Is it an eternal (as in no ending) tree, or is it to be plucked up, axed down, burned up?
Scripture is silent regarding the life of the entire garden, and all we know is we will never see it or the Tree of Life until the new heavens and new earth appear. However, I believe, because of the warning in Ecclesiastes 1:18, unbelievers, non-Christians, and skeptics still figuratively partake of it in their vain attempt to know MORE than God, and their rebellious desire to elevate their knowledge above God's Word.
Such still to this day, demonstrates the limits of the creature, for not a single soul has ever achieved immortality, infallibility, or righteousness through knowledge alone.
Only God's power and grace can provide creaturely access to His spiritual and heavenly heights.