The possibility for confusion in Revelation 17 is rather significant. Yet, in the end, I believe that the interpretation is fairly clear.
First, the ten horns of Daniel 7 are the seven heads of Revelation 17. The reason this works is that the kings (emperors) or Rome are Augustus, Tiberius, Claudius, Caligula, Nero, (Galba, Otho, Vitellius) Vespasian, and Titus. The eleventh horn is the eighth head of Revelation 17. He is the one who “yet will come up out of the Abyss.” This is Domitian. He is a future king in Revelation 17. The immediate context of Revelation is the persecutions of Domitian. These began in AD 96-97. Domitian is the one who began empire-wide persecutions and the one who made Christianity an outlawed religion. The difference between the seven of Revelation 17 and the ten of Daniel 10 is that when you count the emperors of Rome, there is some question as to whether one should even count Galba, Otho and Vitellius. What happened is that in AD 68, when Nero died, it marked the end of the Julian/Claudian dynasty, as there were no male heirs. In the years 68 and 69 three Roman generals were declared emperor by their troops. Neither of the three ever ruled over the entire empire. Therefore to call them “kings” or emperors is debatable. It was only when Vespasian returned to Rome in later AD 69 from Jerusalem that an emperor rose who would rule all of Rome. Vespasian had surrounded Jerusalem and was in the process of putting down the Jewish rebellion when Nero died. His son, Titus, stayed at Jerusalem, finally completing the destruction of Jerusalem in AD 70. I am sure you know about that.
Meanwhile, Vespasian’s younger son, Domitian had remained behind in Rome. He was involved in the battle of Vespasian’s allies to defeat Vitellius. All of this is found in Suetonius’ book about the Roman kings. Domitian is the one who tried to change the set times and the law (Daniel 7). He changed October into Domitianus and November into Germanius (his second name). He abolished the Roman law and established the Domitian law. He helped to defeat the three kings who were eventually replaced by his father Vespasian (Daniel 7). That Domitian is the eleventh horn of Daniel is about as certain as the historical fulfillment of any prophecy from the Old Testament.
All that relates to Daniel 7, but it also helps to explain Revelation 17. The one who was (Rev 17:8) was the persecutor Nero. Nero was the first Roman emperor to execute Christians, but his persecution, although very intense, was of a fairly short duration and was limited to Rome as far as we know. The one who now is not (persecuting the church) is either Vespasian or Titus or both. The one who is yet to come is Domitian. This is the only way I know of to make sense of Revelation 17 and Daniel 7 at the same time.
Here is what makes this confusing, at least somewhat, to me. We know that John was on Patmos in exile when he received the Apocalypse. Therefore, most assume that he was experiencing the persecution of Domitian. However, Revelation clearly represents the persecution of Domitian as in the near future (Rev 1:1). It is not impossible that John was sent into exile by a local ruler before the great persecution began. This seems to be the context of Revelation. My conclusion is that Revelation was given, either during the reign of Titus (AD 79-81) or during the reign of Domitian, but before he began his empire-wide persecution. This would put the date between 81 and 95 AD. Either works. If Domitian was emperor, but had not yet begun to persecute Christians, then we could say that the beast “now is not.”
External evidence from early church fathers point to Revelation having been written during the reign of Domitian, not Titus. This is what Eusebius says, and he does quote his sources (I believe it is Papias, but I am being too lazy to look this up right now ?). He could be wrong, as he wrote more than two hundred years later. Or he could be right and the reign of the eighth king had started, but the beast “now is not” because his persecution had not yet begun. In any case, Domitian is the eight head of Revelation 17 and the eleventh horn of Daniel 7. Of this, I am quite confident.
Does this make sense to you?