The beast, which you saw, once was, now is not, and will come up out of the Abyss and go to his destruction. The inhabitants of the earth whose names have not been written in the book of life from the creation of the world will be astonished when they see the beast, because he once was, now is not, and yet will come. “This calls for a mind with wisdom. The seven heads are seven hills on which the woman sits. 10 They are also seven kings. Five have fallen, one is, the other has not yet come; but when he does come, he must remain for a little while. (Revelation 17:8–10, NIV 1984).
My Musings – This reference to the beast (the anti-Christ) as “once was, now is not, and will come” may be a parody on the divine name in Revelation 1:4 (“from him who is, and who was, and who is to come”). The fact that the beast was, now is not, and will come again in the future may also be a reference to Revelation 13:3 (“One of the heads of the beast seemed to have had a fatal wound, but the fatal wound had been healed. The whole world was astonished and followed the beast”).
The beast (anti-Christ) … “will come up out of the Abyss,” the place from which demons come (Revelation 9:1–2, 11). This indicates that the power behind the beast is satanic (Revelation 13:4) and that Satan and the man he controls are closely identified with one another. Their power is one. The supernatural revival of this future world ruler parallels the revival of his empire (Rome or Babylon once was, now is not, but will once again come up out of the Abyss).
As noted, the period that the beast “is not” could be the time during which it has the fatal wound. With the healing of its wound, it ascends out of the bottomless pit. The beast and the world power he rules returns worse than ever. Its power is derived from Satan (Revelation 11:7), not merely from the sea of convulsed nations (Revelation 13:1).
John is told that the seven heads represent seven mountains (Revelation 17:9) and seven kings or kingdoms (Revelation 17:10). He is not explicitly told the identity of the kings or kingdoms; in fact, it is difficult to determine which he is speaking about (kings or kingdoms).
Could Be Kingdoms – The five kingdoms that had fallen could be the five great dynasties of the past (from John’s perspective) – Egypt, Assyria, Babylon, Persia, and Greece. The kingdom that is would most likely be Rome in John’s day. The one yet to come, the seventh, is likely the future kingdom of the Beast.
Could Be Kings – If John was incarcerated on Patmos during the reign of Nero, the reference to “seven kings,” of whom “five have fallen, one is, and the other has not yet come,” fits nicely with the emperors of Rome. Nero was sixth in the line of Roman emperors. Five had fallen (Julius, Augustus, Tiberius, Caligula, and Claudius), one is (Nero), and the other had not yet come (one of the successive Caesars or a far future anti-Christ?).
Could Be Both – In Scripture, “kings” and kingdoms are often (not always) used interchangeably because kingdoms are generally personified by one prominent head. For Babylon, it was Nebuchadnezzar. For Media-Persia, it was Cyrus. For Greece, it was Alexander the Great. Thus, it is difficult at times to determine whether John is speaking about the individual beast (The anti-Christ), the kingdom of the beast (Babylon or Rome revived) or both (since they are so connected).
My Advice – And the Kingdom of God is personified by Christ, “became flesh and made his dwelling among us.” (John 1:14, NIV 1984). “[His] kingdom is not of this world. If it were, [we] would fight [for it.” (John 18:36, NIV 1984). As it is now, so will it be then. “[A] struggle [that] is not against flesh and blood, but against the rulers, against the authorities, against the powers of this dark world and against the spiritual forces of evil in the heavenly realms.” (Ephesians 6:12, NIV 1984). And out of the abyss. So how do we fight? “Though we live in the world, we do not wage war as the world does. 4 The weapons we fight with are not the weapons of the world. On the contrary, they have divine power to demolish strongholds.” (2 Corinthians 10:3–4, NIV 1984). True today, and it will be true then. Unfortunately, too many of us today are fighting spiritual battles “as the world does.” Brothers and sisters, this should not be.
Sources:
Barry, J. D., Heiser, M. S., Custis, M., Mangum, D., & Whitehead, M. M. (2012). Faithlife Study Bible (Re 17:8). Bellingham, WA: Logos Bible Software.
Walvoord, John F. (1985). Revelation. In J. F. Walvoord & R. B. Zuck (Eds.), The Bible Knowledge Commentary: An Exposition of the Scriptures (Vol. 2, p. 971). Wheaton, IL: Victor Books.
Jamieson, R., Fausset, A. R., & Brown, D. (1997). Commentary Critical and Explanatory on the Whole Bible (Vol. 2, p. 591-592). Oak Harbor, WA: Logos Research Systems, Inc.
Wiersbe, W. W. (1992). Wiersbe’s expository outlines on the New Testament (p. 845). Wheaton, IL: Victor Books.
Sloan, R. B. (1998). The Revelation. In D. S. Dockery (Ed.), Holman concise Bible commentary (p. 661). Nashville, TN: Broadman & Holman Publishers.

Your conjectures about the “Could Be Kingdoms” and the “Could Be Kings” and the “Could Be Both” were quite interesting. Thank you.
LikeLike