1. History
From the time of Christ to the time of the fourth century (Constantine) there had been an intense persecution of Christians, both by the Jews and by the Romans. In the time of Peter it was by Nero. It the time it was by Domitian. After Domitian the persecution was carried on by other cruel dictators until Christianity became legalized by Constantine who used it for his own political gain.
Thus whether John was looking backward or forward there would have been persecution, no matter what the date you assign it. Read Peter, written previous to the destruction of Jerusalem. The persecution was very intense. And then Domitian. He was no less cruel.
2. Purpose of John.
The purpose was two-fold. The book was apocalyptic designed to tell of events to come. The key verse is given in vs. 19
Write the things which thou hast seen, and the things which are, and the things which shall be hereafter; (Revelation 1:19)
--The book is divided into three parts: the past, present, and future.
The present were the churches. The future started in chapter six.
Now, why those churches. I believe that the Holy Spirit chose those particular churches because of their particular problems. The Bible is a timeless book. It is applicable to every age. Jesus chose those churches with a wide range of problems that we, in every age, would be able to relate to, and would teach us. It is not an accident that those particular churches were chosen above others. It was the Holy Spirit's choosing.
3. John's age.
John was the youngest of all the apostles and outlived them all. His death may have been in the beginning of the second century. It makes sense that his books would have been written in the 90's. One of John's purposes in writing is to write supplemental information to that which was already written in the "synoptic gospels" (Matthew, Mark, and Luke), which had already been written well aforetime. The gospel of John stands out alone as uniquely different in this way, giving much different information than the other gospels and a different perspective as well. This is another argument for the Book of Revelation's late date.
John was exiled to the Isle of Patmos. It was there that he wrote Revelation, as the first chapter indicates. History tells us that it was under the rule of Domitian that he was exiled there. That should be fairly conclusive proof that this book has a late date:
I John, who also am your brother, and companion in tribulation, and in the kingdom and patience of Jesus Christ, was in the isle that is called Patmos, for the word of God, and for the testimony of Jesus Christ. (Revelation 1:9)