The original question correctly recognizes that in the NT, οἰκουμένη most often appears to refer to the Roman empire, but then incorrectly sees this as an indication that Jesus' prediction about the end following upon the testimony to the empire. The solution is not to change the referent of οἰκουμένη to the leavening of the entire planet but instead, correctly identifying what the "end" was the end of.
οἰκουμένη in the NT:
[Mat 24:14 YLT] (14) and this good news of the reign shall be proclaimed in all the world, for a testimony to all the nations; and then shall the end arrive.
[Luk 2:1 YLT] (1) And it came to pass in those days, there went forth a decree from Caesar Augustus, that all the world be enrolled --
[Luk 4:5 YLT] (5) And the Devil having brought him up to an high mountain, shewed to him all the kingdoms of the world in a moment of time,
[Luk 21:26 YLT] (26) men fainting at heart from fear, and expectation of the things coming on the world, for the powers of the heavens shall be shaken.
[Act 11:28 YLT] (28) and one of them, by name Agabus, having stood up, did signify through the Spirit a great dearth is about to be throughout all the world -- which also came to pass in the time of Claudius Caesar --
[Act 17:6, 31 YLT] (6) and not having found them, they drew Jason and certain brethren unto the city rulers, calling aloud -- 'These, having put the world in commotion, are also here present, ... (31) because He did set a day in which He is about to judge the world in righteousness, by a man whom He did ordain, having given assurance to all, having raised him out of the dead.'
[Act 19:27 YLT] (27) and not only is this department in danger for us of coming into disregard, but also, that of the great goddess Artemis the temple is to be reckoned for nothing, and also her greatness is about to be brought down, whom all Asia and the world doth worship.'
[Act 24:5 YLT] (5) for having found this man a pestilence, and moving a dissension to all the Jews through the world -- a ringleader also of the sect of the Nazarenes --
[Rom 10:18 YLT] (18) but I say, Did they not hear? yes, indeed -- 'to all the earth their voice went forth, and to the ends of the habitable world their sayings.'
[Heb 1:6 YLT] (6) and when again He may bring in the first-born to the world, He saith, 'And let them bow before him -- all messengers of God;'
[Heb 2:5 YLT] (5) For not to messengers did He subject the coming world, concerning which we speak,
[Rev 3:10 YLT] (10) 'Because thou didst keep the word of my endurance, I also will keep thee from the hour of the trial that is about to come upon all the world, to try those dwelling upon the earth.
[Rev 12:9 YLT] (9) and the great dragon was cast forth -- the old serpent, who is called 'Devil,' and 'the Adversary,' who is leading astray the whole world -- he was cast forth to the earth, and his messengers were cast forth with him.
[Rev 16:14 YLT] (14) for they are spirits of demons, doing signs -- which go forth unto the kings of the earth, and of the whole world, to bring them together to the battle of that great day of God the Almighty; --
To my mind, every one of these instances maps best to the Empire rather than "the planet".
So I turn to the question of, "the end of what"?
I propose that what is in view is the end of the age of the Sinai covenant brought about by the destruction of the Jerusalem temple, Jerusalem itself and the Jerusalem temple Sinai covenant based theocratic polity:
[Mat 13:39, 49 YLT] (39) and the enemy who sowed them is the devil, and the harvest is a full end of the age, and the reapers are messengers. ... (49) so shall it be in the full end of the age, the messengers shall come forth and separate the evil out of the midst of the righteous,
[Mat 24:3 YLT] (3) And when he is sitting on the mount of the Olives, the disciples came near to him by himself, saying, 'Tell us, when shall these be? and what [is] the sign of thy presence, and of the full end of the age?'
[Mat 28:20 YLT] (20) teaching them to observe all, whatever I did command you,) and lo, I am with you all the days -- till the full end of the age.'
[Isa 47:7 YLT] (7) And thou sayest, 'To the age I am mistress,' While thou hast not laid these things to thy heart, Thou hast not remembered the latter end of it.
[Eze 35:5 YLT] (5) Because of thy having an enmity age-during, And thou dost saw the sons of Israel, By the hands of the sword, In the time of their calamity, In the time of the iniquity of the end:
[Mat 13:40 YLT] (40) 'As, then, the darnel is gathered up, and is burned with fire, so shall it be in the full end of this age,
[1Co 10:11 YLT] (11) And all these things as types did happen to those persons, and they were written for our admonition, to whom the end of the ages did come,
[Heb 9:26 YLT] (26) since it had behoved him many times to suffer from the foundation of the world, but now once, at the full end of the ages, for putting away of sin through his sacrifice, he hath been manifested;
It is also the time of a new covenant:
[Jer 31:31 YLT] (31) Lo, days are coming, an affirmation of Jehovah, And I have made with the house of Israel And with the house of Judah a new covenant,
[Mat 26:28 YLT] (28) for this is my blood of the new covenant, that for many is being poured out -- to remission of sins;
[Mar 14:24 YLT] (24) and he said to them, 'This is my blood of the new covenant, which for many is being poured out;
[Luk 22:20 YLT] (20) In like manner, also, the cup after the supping, saying, 'This cup [is] the new covenant in my blood, that for you is being poured forth.
[1Co 11:25 YLT] (25) In like manner also the cup after the supping, saying, 'This cup is the new covenant in my blood; this do ye, as often as ye may drink [it] -- to the remembrance of me;'
[2Co 3:6 YLT] (6) who also made us sufficient [to be] ministrants of a new covenant, not of letter, but of spirit; for the letter doth kill, and the spirit doth make alive.
[Heb 8:8 YLT] (8) For finding fault, He saith to them, 'Lo, days come, saith the Lord, and I will complete with the house of Israel, and with the house of Judah, a new covenant,
[Heb 9:15 YLT] (15) And because of this, of a new covenant he is mediator, that, death having come, for redemption of the transgressions under the first covenant, those called may receive the promise of the age-during inheritance,
[Heb 12:24 YLT] (24) and to a mediator of a new covenant -- Jesus, and to blood of sprinkling, speaking better things than that of Abel!
So the problem is not that of a failed prediction but of faulty expectations. Christ came and brought the end, and the new beginning:
[2Co 5:17 YLT] (17) so that if any one [is] in Christ -- [he is] a new creature; the old things did pass away, lo, become new have the all things.
[Gal 6:15 YLT] (15) for in Christ Jesus neither circumcision availeth anything, nor uncircumcision, but a new creation;
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