Yes they have been planning this for years, but will never come to be as the temple that is mentioned in 2 Thessalonians 2:6 is that temple (not actual temple, but control) of power that the son of perdition will take as trying to be like God in all His power thinking himself higher than God. The withholding is that of the son of perdition (man of sin) who causes a great falling away from truth and will be exposed and then the day of the Lord will come.
The abomination of desolation Daniel spoke of was literal of the destruction of Jerusalem and prophetic of the destruction of those who are in Christ when the son of perdition sets up his ruling power as then there will be great tribulation (not a so called 7 year Great Tribulation which is not found in scripture) as never seen before or ever will be for this abomination will usher in the day of the Lord as there will be a falling away from truth as never has been before or ever will be.
Mat 24:15 When ye therefore shall see the abomination of desolation, spoken of by Daniel the prophet, stand in the holy place, (whoso readeth, let him understand
Mat 24:21 For then shall be great tribulation, such as was not since the beginning of the world to this time, no, nor ever shall be.
Mat 24:27 For as the lightning cometh out of the east, and shineth even unto the west; so shall also the coming of the Son of man be.
Mat 24:28 For wheresoever the carcase is, there will the eagles be gathered together.
Mat 24:29 Immediately after the tribulation of those days shall the sun be darkened, and the moon shall not give her light, and the stars shall fall from heaven, and the powers of the heavens shall be shaken:
Mat 24:30 And then shall appear the sign of the Son of man in heaven: and then shall all the tribes of the earth mourn, and they shall see the Son of man coming in the clouds of heaven with power and great glory.
Mat 24:31 And he shall send his angels with a great sound of a trumpet, and they shall gather together his elect from the four winds, from one end of heaven to the other.
Mat 24:36 But of that day and hour knoweth no man, no, not the angels of heaven, but my Father only.
Mat 24:37 But as the days of Noe were, so shall also the coming of the Son of man be.
2Th 2:1 Now we beseech you, brethren, by the coming of our Lord Jesus Christ, and by our gathering together unto him,
2Th 2:2 That ye be not soon shaken in mind, or be troubled, neither by spirit, nor by word, nor by letter as from us, as that the day of Christ is at hand.
2Th 2:3 Let no man deceive you by any means: for that day shall not come, except there come a falling away first, and that man of sin be revealed, the son of perdition;
2Th 2:4 Who opposeth and exalteth himself above all that is called God, or that is worshipped; so that he as God sitteth in the temple of God, shewing himself that he is God.
2Th 2:5 Remember ye not, that, when I was yet with you, I told you these things?
2Th 2:6 And now ye know what withholdeth that he might be revealed in his time.
2Th 2:7 For the mystery of iniquity doth already work: only he who now letteth will let, until he be taken out of the way.
2Th 2:8 And then shall that Wicked be revealed, whom the Lord shall consume with the spirit of his mouth, and shall destroy with the brightness of his coming:
2Th 2:9 Even him, whose coming is after the working of Satan with all power and signs and lying wonders,
2Th 2:10 And with all deceivableness of unrighteousness in them that perish; because they received not the love of the truth, that they might be saved.
2Th 2:11 And for this cause God shall send them strong delusion, that they should believe a lie:
2Th 2:12 That they all might be damned who believed not the truth, but had pleasure in unrighteousness.