Suggested in the past:
People who died in the flood
People who died at Sodom and Gomorrah
Religious leaders of Jesus day who died without repenting
People who die at Armageddon
(Once believed that people who died between 1914 and Armageddon who weren't jws would go to Gehenna since it was a judgment period. That changed when the WTS determined that the sheep and the goats were not to be separated until after the great tribulation started)
*** w82 4/1 p. 27 par. 6 Survival or Destruction at the "Great Tribulation"
Now, the Bible definitely shows that some end up in the symbolic Gehenna before the 1,000-year Judgment Day begins. Jesus told the unrepentant scribes and Pharisees that they and their Gentile proselytes were ‘subjects for Gehenna’ or, literally, ‘sons of Gehenna.’ (Matthew 23:15, 33-35; see also John 9:39-41; 15:22-24.) If even a proselyte of the Pharisees became a subject for Gehenna ‘twice as much so as themselves,’ how much more so Judas Iscariot, who made a heinous deal with them to betray God’s Son! Jesus implied this when he called Judas "the son of destruction." (John 17:12) Similarly, unrepentant apostates go, at death, not to Sheol, or Hades, but to Gehenna. (Hebrews 6:4-8; 2 Peter 2:1) The same is true of dedicated Christians who persist in willful sin or those who "shrink back." (Hebrews 10:26-31, 38, 39) These are merely examples to show that some, even in "this system of things," have committed the sin for which there is no forgiveness, not even in the system of things "to come." (Matthew 12:31, 32; compare 1 John 5:16.) They will, therefore, not be resurrected
w05 5/1 pp. 16-17 Who Will Be Resurrected?
Who Are in Gehenna?
Compare David’s situation with that experienced by the Greater David, Jesus. One of Christ’s 12 apostles, Judas Iscariot, turned traitor like Ahithophel. Judas’ treacherous act was far more serious than that of Ahithophel. Judas acted against God’s only-begotten Son. In a prayer at the end of his earthly ministry, God’s Son reported about his followers: "When I was with them I used to watch over them on account of your own name which you have given me; and I have kept them, and not one of them is destroyed except the son of destruction, in order that the scripture might be fulfilled." (John 17:12) By here referring to Judas as "the son of destruction," Jesus indicated that when Judas died, there was no hope of a return for him. He did not live on in God’s memory. He went, not to Sheol, but to Gehenna. What is Gehenna?
Jesus condemned the religious leaders of his day because they made each of their disciples "a subject for Gehenna." (Matthew 23:15) Back at that time, people were familiar with the Valley of Hinnom, an area used as a garbage dump where bodies of executed criminals who were deemed unworthy of a proper burial were deposited. Earlier, Jesus himself had made mention of Gehenna in his Sermon on the Mount. (Matthew 5:29, 30) Its symbolic meaning was clear to his listeners. Gehenna represented complete destruction without hope of a resurrection. Apart from Judas Iscariot of Jesus’ day, have others gone to Gehenna rather than to Sheol, or Hades, at their death?
The first humans, Adam and Eve, were created perfect. Their fall into sin was deliberate. Before them was either everlasting life or death. They disobeyed God and sided with Satan. When they died, they had no prospect of benefiting from Christ’s ransom sacrifice. Rather, they went to Gehenna.
Adam’s firstborn son, Cain, murdered his brother Abel and thereafter lived as a fugitive. The apostle John described Cain as one "who originated with the wicked one." (1 John 3:12) It is reasonable to conclude that like his parents, he went to Gehenna when he died. (Matthew 23:33, 35) What a contrast this is with the situation of righteous Abel! "By faith Abel offered God a sacrifice of greater worth than Cain, through which faith he had witness borne to him that he was righteous, God bearing witness respecting his gifts," explained Paul, adding, "and through it he, although he died, yet speaks." (Hebrews 11:4) Yes, Abel is presently in Sheol awaiting a resurrection.
Then there is the concept of special "judgment periods."
*** w60 1/15 pp. 52-53 This Is a Time of Judgment
There have been certain periods in human history when Jehovah God has turned his attention toward the earth for judgment. The people he put under surveillance were judged by their course of action toward his righteous principles and purposes. The first human pair, for example, were under divine judgment, but their bad conduct brought them a sentence of death.
The people who lived immediately before the flood of Noah’s day passed through a judgment period that ended when the Flood swept most of them out of existence. Because of their wicked disregard for God and his purposes he judged them adversely. "He did not hold back from punishing an ancient world, but kept Noah, a preacher of righteousness, safe with seven others when he brought a deluge upon a world of ungodly people."—2 Pet. 2:5.
There is nothing in the Bible to suggest that these people were or shall be punished in a fiery hell. From the time of Adam to this very day the punishment for wickedness has not been conscious torment in a fiery hell but rather death—a cutting off from life. "For the wages sin pays is death." "Jehovah is guarding all those loving him, but all the wicked ones he will annihilate."—Rom. 6:23; Ps. 145:20.
After mentioning the world destroyed by the Flood and the cities of Sodom and Gomorrah that were destroyed by fire, Peter states: "Jehovah knows how to deliver people of godly devotion out of trial, but to reserve unrighteous people for the day of judgment to be cut off." (2 Pet. 2:9) These two outstanding judgment periods were proofs of this. The wicked people in each period were reserved, or allowed to remain, throughout their judgment periods until the day of their execution. But persons of godly devotion who had received a favorable judgment were preserved.
These judgment periods are examples for us. They are prophetic pictures of the great judgment period in which we now live. Jesus himself pointed this out when he said: "Just as it occurred in the days of Noah, so it will be also in the days of the Son of man . . . Likewise, just as it occurred in the days of Lot."—Luke 17:26, 28.
*** w52 6/1 p. 341-50 Fixing Destinies in This Judgment Period