We appear to be on the same (or, at least, a similar) page with regard to death of the old life, the new life, the necessity of genuine mourning, the paradigmatic passion of Christ, and participation in the life and work of God. In short, we continue to find considerable convergence in our applications of a given scripture passage, even though we approach it from different starting places.
That being said, I want to try to clarify my take on a few matters.
First, I (along with most modern commentators)do not think Jesus propounded a new idea via the beatitude. I apologize for giving such an impression. Isaiah 61 almost undoubtedly informed his understanding of himself and his mission. I have no doubt the other passages you mention did the same. We agree, I think, that Jesus was genuinely a first century Jew, who drew upon the traditions and teachings of his heritage to frame his message and work.
No doubt I need to clarify what I had in mind when I wrote of Jesus "turning normal expectations upside down." Start with the first century. First century Judaism, as I understand the matter, was far from monolithic with regard to concepts of the (or "a") Messiah's role or the desired results of a messiah's work. Jesus' understanding (label it the Isaiah option)had a long history and could be found among the population.
Other options existed as well. For example, the Zealots seem to have thought in term of a military/political messiah figure who would defeat the Romans and reestablish the old Davidic kingdom (at least as they imagined that kingdom to have been). The apostles sometimes seem to exemplify a vision of the Messiah that leaves little if any room for suffering, let alone death. The Essenes, insofar as I can tell, seem to have envisoned a great war in which the Children of Light joined with God to make God's enemies (and theirs) suffer! On and on it goes. It seems the more we learn about the first century Jewish world, the more complicated the picture becomes.
My point, then, is that Jesus' take certainly upended the expectations of a sizable percentage of first century Jewish listeners, not because it was exclusive to him but because they did not share (at first)his perspective. Obviously, when the beatitudes moved out into first century gentile cultures, they ran counter to normal expectations. As for our own time, it seems to me that the beatitudes, including the one in question, challenge typical American assumptions about happiness.
Historical matters aside, taken seriously the beatitude (and its companions)ought to frighten us a bit. They vie to replace our survival instinct with something quite different: willing reliance upon and identification with God and the the ways of God. Such a life makes little sense to most of the world at any time, which seldom takes seriously anything other than defensive or coercive power.