"What, in your opinions was the significance of the prophecy of Jesus in the Olivet Discourse concerning the destruction of the Temple in Jerusalem....and its extra-Biblical fulfillment in AD 70?"
The fulfillment of Jesus' end-times prophecies began to come into being in the first century. This is confirmed by the use of the word "ginomai" when He described the events that are commonly called "the Olivet Discourse".
By the use of the word, ginomai", I see it as a lengthly series of events which began at that time, not completed at that time.........which if completion was the issue a different word other than ginomai would have been used.......teleoo, or, pleroo, or an associated word commonly linked with fulfillment.
The destruction of the Temple signified the inauguration of a new ministry by Jesus, as a priest after the order of Melchezedek, which He is currently fulfilling having begun them when He ascended into heaven.
While the first (tabernacle) remained standing, there could not be two simultaneous ministries by priests as Jesus ministers in the heavenly tabernacle not made with hands.
I do not see the destruction of the temple as a judgment to end the nation of Israel as He, Jesus, had asked for their forgiveness on the Cross.
They (Israel) became enemies of the gospel having been blinded of God (for our sakes so that we could be delivered the gospel).....but.....they remain "beloved for the father's sakes". They (Israel) will remain "enemies" until the blindness is removed.....at which point....."all Israel shall be saved".
For I am persuaded, that neither death, nor life, nor angels, nor principalities, nor powers, nor things present, nor things to come, Nor height, nor depth, nor any other creature, shall be able to separate us from the love of God, which is in Christ Jesus our Lord. Romans 8:38,39