Try this on for size,
Joh 1:14 And the Word was made flesh, and dwelt among us, (and we beheld his glory, the glory as of the only begotten of the Father,) full of grace and truth.
My understanding in oneness Jesus was the expression of God made flesh. Or God in a fleshly blody. However one wants to discribe it is alright by me. the point here is that while on earth we knew this body as the "Son of God" or "the only begotten of teh father" In other words in this time of life God presented himself in a bodily form born of a women and called himself the son of God.
God being a spirit being cannot be seen unless he presents himself in a form that is tangeble or visible. I beleive the term is theophany but don't quote me on that. Anyway as I see it the body of Jesus is the final presentation God makes himself know to mankind. When in Corinthians the son becomes subject to God simply means, he will no longer be known as the son, as the redemptive work of the son will be finished, instead we will see him as he is from the foundation of the world. God will be all in all, Jesus is the only body of God we will ever see. We will see him then as God.
Just my thoughts