Maybe I am being stupid. I don't see how a physical city is precluded by it being the Church.
We simply have moved from the buildings (the temple) being the defining characteristic, to the people (believers) being the defining characteristic.
Because the time of reformation has come, we no longer look to the ceremonial laws that pointed ahead to the time of reformation. On this side of it believers are considered the temple of God. The way to the Holy of Holiness using those metaphors that made up the temporal was no longer needed. God who has no form was no longer being represented by that seen.
Right from the beginning we can see the Bible using architectural metaphors to describe His wife the church. Cities in respect to the residents were built to show that who they are founded after, Cain became the founder of the City Canaan, as the Canaanites .Philippi became the founder of the city of the Philippians as to the residents that make it up. Just as Enoch
Gen 4:17 And Cain knew his wife; and she conceived, and bare Enoch: and he builder a city, and called the name of the city, after the name of his son, Enoch.
While God has named His people, His bride, Christian, named after His Son Christ, the new name
He named His people because the time of reformation had come. Giving us a better understanding how cites relate to souls as residents thereof.
The New Jerusalem not seen, the city of Christ is shown prepared as His bride. He describes the heavenly Jerusalem as the married land. And as in all parables it is represented by the temporal land as that seen the earthly Jerusalem.
2Co 4:18 While we look not at the things which are seen, but at the things which are not seen: for the things which are seen are temporal; but the things which are not seen are eternal.
When looking at Mark we are informed by the Spirit of Christ ,that whenever Christ brought the gospel He spoke in parables using the temporal things of this world, as that seen to speak of the eternal as that not seen. The faith principle needed to rightfully divide His spiritual truths. And therefore without a parable He spoke not.
Since Christ is eternal God not seen He is the sole author of the Bible. I believe we should anticipate searching for the hidden meaning as the kind of language God has designed. We can expect while we are given historical information of events that did occur there is another understanding (spiritual) hidden from natural unconverted men.
Like for instance when Christ would perform a miracle. The miracle actually happened but again the spiritual significance is hid from the lost and therefore through a miracle He is teaching us the very nature of salvation.(not seen)
I would be careful with those who insist we dismiss the spiritual understand for one that would be literal, as if the kingdom of God was of this world. And the temporal has already become the eternal, as if the kingdom of God was of the world