You are right, Jon, about the countless speculative opinions regarding prophecies and the building of a third temple in Jerusalem. Many of the implications of such interpretations seem bizarre, in terms of both religion and politics.

I've heard and read of efforts to produce or accumulate appropriate ceremonial artifacts in anticipation of a rebuilt temple. I've seen pictures that are purported to be of golden objects prepared for renewed temple service. Recent news stories related a request by certain Jewish authorities to the pope for the privilege of scouring the storehouses of the Vatican for temple artifacts carried to Rome in the first century, including perhaps the seven branched lampstand. Some people at least take the idea of building a third Jewish temple very seriously.

Considering the problems of priestly credentials even in Ezra's day (see Ezra 2:62), how much confidence could be placed in the names Cohen and Levi in setting up priestly and Levitical orders? Perhaps genetic testing would be the criterion, but while that might establish relationships tenuously, many questions would remain. Considering the seriousness of genealogical qualifications in the Old Testament, it seems rather dubious.

There were news articles a few years ago about a "red heifer" born in Israel, but not quite red enough, which would be necessary for cleansing ceremonies. Would a new temple be cleased with blood, when Judaism has moved completely away from ritual sacrifices and into symbolic substitutes of prayers and readings and so forth? Would a bronze altar be built for sacrificial service, and animals slaughtered for thanksgiving and atonement? Renewing animal sacrifices would seem to be highly dubious in this generation, but what substitutes would make a temple acceptable and meaningful?

What would have to happen to make space on the temple mount without starting World War III? A few interpreters have argued for the Dome of the Rock being the third temple. Some have argued for a sort of ecumenical temple of all nations, where Jews, Moslems and Christians come together in peace. Is that what Isaiah 2 is picturing?

On the other hand, the New Testament seems to consistently interpret passages some would apply to a future temple to the church Jesus purchased with his blood. As Paul observed, "What agreement has the temple of God with idols? For we are the temple of the living God; as God said," (2 Cor 6:16a ESV). Jesus promised a permanent place in the structure of God's temple to the overcomers in the Philadelphian church (The one who conquers, I will make him a pillar in the temple of my God. Never shall he go out of it, and I will write on him the name of my God, and the name of the city of my God, the new Jerusalem, which comes down from my God out of heaven, and my own new name. Rev 3:12 ESV)

Paul describes the church, consisting of all the redeemed of every nation, this way in Eph 2:19-22
19 So then you are no longer strangers and aliens, but you are fellow citizens with the saints and members of the household of God, 20 built on the foundation of the apostles and prophets, Christ Jesus himself being the cornerstone, 21 in whom the whole structure, being joined together, grows into a holy temple in the Lord. 22 In him you also are being built together into a dwelling place for God by the Spirit. ESV

By the same token, language describing features of Ezekiel's visionary temple (Ezek 40-47) is sometimes echoed in the description of the heavenly Jerusalem, a spiritual dwelling place, in Rev 21-22. Christians are enjoined to go to Jesus "outside the camp" (Hebrews 13:13) in a comparison/contrast with temple ritual. In fact, in its many points about the fulfillment of tabernacle and temple symbolism in the New Covenant of Jesus, Hebrews asserts that Jesus, the great high priest, could not serve at an earthly sanctuary, because he is born of the wrong tribe (Hebrews 7:12-14), and that the Old Covenant temple priesthood and practice are not a part of the New Covenant (Hebrews 13:9-10).

Isaiah 2:2-5 speaks prophetically of the Messiah's kingdom, and talks about all nations coming to the mountain of the LORD and the house of the God of Jacob. Hebrews 12:22 (and context, 18-24) describes the house of God in terms of Mount Zion, the heavenly Jerusalem, and the church of the firstborn, among other terms. Paul identifies the house of God (or household) as the church, the pillar and ground of truth (1 Tim 3:15).

When Jesus spoke of the abomination of desolation in Matt 24 (etc.) surely his followers understood that as being fulfilled when Titus came to Jerusalem (as Antiochus had done before, only moreso...). The evidence for Christian flight from Jerusalem during those wretched days upholds their undestanding of the warning. If the church embodies God's temple in the last days, and if there is to be another "abomination of desolation", then surely he who sets himself up in God's temple "over everything that is called God" (2 Thessalonians 2:4) is one who exalts himself in or over the church, not someone bringing idolatry into a third Jewish temple. In fact, given the message of fulfillment in Hebrews and Galatians and Romans, it would be hard for me to perceive renewed ritual sacrifice in a third temple as anything but idolatry in itself, exalting something physical over the spiritual work of Christ.