?????
No.
It would make no sense to explain anything to John if it did not matter to John. Explaining non-existent things to John that would have absolutely no bearing on John's life makes both the explanation and the scripture meaningless to John (and his first century audience). It violates one of the most basic precepts in exegesis: first understand the text as the original author and his original first century audience would have understood it! It also goes against the New Testament precedent where all the mysteries where revealed to exist in the NT era.
Matthew 13:11
Jesus answered them, "To you it has been granted to know the mysteries of the kingdom of heaven, but to them it has not been granted.
Romans 11:25-26
For I do not want you, brethren, to be uninformed of this mystery—so that you will not be wise in your own estimation—that a partial hardening has happened to Israel until the fullness of the Gentiles has come in; and so all Israel will be saved; just as it is written...
Romans 16:25-26
Now to Him who is able to establish you according to my gospel and the preaching of Jesus Christ, according to the revelation of the mystery which has been kept secret for long ages past, but now is manifested, and by the Scriptures of the prophets, according to the commandment of the eternal God, has been made known to all the nations, leading to obedience of faith;
1 Corinthians 2:6-7
Yet we do speak wisdom among those who are mature; a wisdom, however, not of this age nor of the rulers of this age, who are passing away; but we speak God's wisdom in a mystery, the hidden wisdom which God predestined before the ages to our glory;
1 Corinthians 4:1
Let a man regard us in this manner, as servants of Christ and stewards of the mysteries of God.
1 Corinthians 15:51-52
Behold, I tell you a mystery; we will not all sleep, but we will all be changed, in a moment, in the twinkling of an eye, at the last trumpet; for the trumpet will sound, and the dead will be raised imperishable, and we will be changed.
Colossians 1:25-27
Of this church I was made a minister according to the stewardship from God bestowed on me for your benefit, so that I might fully carry out the preaching of the word of God, that is, the mystery which has been hidden from the past ages and generations, but has now been manifested to His saints, to whom God willed to make known what is the riches of the glory of this mystery among the Gentiles, which is Christ in you, the hope of glory.
Colossians 2:1-2
For I want you to know how great a struggle I have on your behalf and for those who are at Laodicea, and for all those who have not personally seen my face, that their hearts may be encouraged, having been knit together in love, and attaining to all the wealth that comes from the full assurance of understanding, resulting in a true knowledge of God's mystery, that is, Christ Himself,
2 Thessalonians 2:7
For the mystery of lawlessness is already at work; only he who now restrains will do so until he is taken out of the way.
1 Timothy 3:16
By common confession, great is the mystery of godliness: He who was revealed in the flesh, was vindicated in the Spirit, seen by angels, proclaimed among the nations, believed on in the world, Taken up in glory.
Revelation 1:20
As for the mystery of the seven stars which you saw in My right hand, and the seven golden lampstands: the seven stars are the angels of the seven churches, and the seven lampstands are the seven churches.
Revelation 10:7
...but in the days of the voice of the seventh angel, when he is about to sound, then the mystery of God is finished, as He preached to His servants the prophets.
That is just a sampling of the NT's use of mystery. They uniformly speak of the mystery revealed and explained, and existing at the time the explanation occurred. You would have us believe this Revelation mention stands in complete distinction from all the other NT precedents, even though Revelation explicitly states,
Revelation 1:3
Blessed is he who reads and those who hear the words of the prophecy, and heed the things which are written in it; for the time is near.
Revelation 1:19
Therefore, write the things which you have seen, and the things which are, and the things which will take place after these things.
Most of Revelation had either already occurred or was occurring at the time it was revealed to John and what remained "after these things" was near.