Fascinating OP.
By coincidence I have just finished reading Hart's
The Light of Tabor: Toward a Monistic Christology, which presents much of the same theme from the perspective of Christology, not anthropology. However much of what Hart concludes about Christ and the Trinity (and the Council of Chalcedon) can be translated into your comments above pertaining to human nature.
For example, for Hart, in the Incarnation, Christ does not merely "inhabit" a human body but rather reveals - as a kind of theophany - what humanity has always been, which is a unified reality in which the material and spiritual are not two substances but two
modes of participation in the divine Logos - which means the creature is also a kind of theophany. In that sense, Christ’s resurrected body is the transfiguration of matter itself - the unveiling of its true, glorified form.
For Hart, divinity and humanity are not two disparate substances which are somehow glued together arbitrarily, as in dualism. They are one reality, one act of divine self-disclosure. Humanity is not composed of separable “parts” (body and soul) but is a single, dynamic participation in the divine Logos. The soul is not a detachable immaterial entity; it is the form of the body, the living unity of the person. Resurrection, therefore, is not the reanimation of a corpse or the liberation of the soul, but the transformation of the whole person into glory - the
completion of what creation already is in its divine ground.
This aligns with the Jewish-Christian monism discussed in the post you shared: the nephesh as “living being,” the resurrection of the whole person, and the affirmation of the body as integral to salvation.
Now, what interests me here is the difference of this view with the Catholic metaphysics, and whether there really is any. According to Aquinas, for example, the divine essence cannot become visible as though it were a color or a form. Visibility belongs to created being, which receives and manifests divine light according to its capacity. For Aquinas we do participate in the divine realm but it is a participation by
analogy, not by identity. If we say creature and Creator are one in substance, we dissolve the contingency of creation and, in a way, make the Incarnation meaningless. After all, if there is identity without difference, why would we have needed an Incarnation? The creature’s finitude is therefore not an illusion to be dispelled but a perfection to be fulfilled.
Having said this Aquinas himself comes very close to your own view when it comes to anthropology, not Christology - he
does seem to state explicitly that the human person is
not two things (soul and body) but one substance, and that the soul is the
form of the body, and he bases his argument on Aristotle. ST I.76.1 is where he does this. It is an extremely long Article so I should not post it.
In that Article, he states that the human being is a single substantial unity, composed of body and soul. The soul is the form that gives life and identity to the body. Although the soul has an immaterial, subsistent nature, it does not use the body like a tool - rather, it informs it from within. Thus, human nature is neither purely material nor purely spiritual, but a single composite of both.