I believe that ultimate universal reconciliation is a foundation doctrine. It is the sum, actually of two of the six foundation doctrines listed in Hebrews 6:1,2- The resurrection of the dead and eternal judgment.
The doctrine of eternal judgment is the doctrine of "God's reasons". The "why's" or wisdom of all He has done. It is impossible to represent the I AM while misrepresenting the ultimate reason and purpose for what He has done.
No house can stand tall and true with two of six foundations missing or askew. IMO this is the reason Christianity has stalled out, especially in the western world- where it is a hollow shell and even a caricature of the biblical faith community.
For me UR isnt a tangent or a peripheral revelation.
It is pure milk of the word. It is at the core of the revelation of God's heart and His purpose in creation and His plan for the age. the word "prophecy" comes from a Hebrew word meaning "bubbling over". The testimony of Jesus Christ is the "Spirit of prophecy"- which is the bubbling up as from a well deep in the earth of the pure, clear refreshing Spirit of God- bearing His heart to humanity.
Nothing makes any sense until one realizes that God is reconciling and restoring all things in Christ. The doctrinal mutations required to explain things in the absence of, or in opposition to, these two foundation doctrines have produce some of the greatest strongholds and fortresses that exalt themselves against the true knowledge of God.
That's why I think Tentmaker is the greatest site on the worldwide web. And its the reason why promoting and explaining the Salvation of All has to remain in the forefront of our discussions. It is a holy calling, and it is our core "reason for being" in this internet plane. :o)