I would argue this is where Amillennialism has a more difficult time answering Zechariah 14. The Jerusalem of Zechariah 14:11 is clearly the New Jerusalem
Zechariah 14:11 they shall dwell in the city; and there shall be no more any curse, and Jerusalem shall dwell securely
Revelation 22:2 no longer will there be any curse
So how can their be unbelievers (those that do not go up to Jerusalem to worship nor receive rain) exist after the New Jerusalem?
It seems that revelation 22 has that answer: The New Jerusalem (body of Christ) provides healing for the nations after the city and sanctuary are destroyed.
Revelation 22:2 down the middle of the main street of the city. On either side of the river stood a tree of life, producing twelve kinds of fruit and yielding a fresh crop for each month. And the leaves of the tree are for the healing of the nations.
Revelation 22:15 Outside (the body of Christ; New Jerusalem) are the dogs and sorcerers and the sexually immoral and murderers and idolaters, and everyone who loves and practices falsehood.
Could you remind me where you are placing the time of the NHNE and NJ in Revelation 21-22? Was it before or after the 2nd coming that you place this?
I notice that you acknowledge that these would be unbelievers going up to Jerusalem. That's a plus.
Here's some of my line of thinking, though I expect you to disagree since you apparently don't think a thousand years fits with a time post the 2nd coming.
Isaiah 66:22 For as the new heavens and the new earth, which I will make, shall remain before me, saith the LORD, so shall your seed and your name remain.
23 And it shall come to pass, that from one new moon to another, and from one sabbath to another, shall all flesh come to worship before me, saith the LORD.
24 And they shall go forth, and look upon the carcases of the men that have transgressed against me: for their worm shall not die, neither shall their fire be quenched; and they shall be an abhorring unto all flesh.
The first thing to note, the context makes mention of the NHNE. Verse 23 sounds somewhat like Zechariah 14:16 to me. Notice in verse 24----And they shall go forth, and look upon the carcases of the men that have transgressed against me. What would be the nearest antecedent of they in verse 24? Would it not be all flesh that shall come to worship before Him?
Try looking at it like the following then.
And it shall come to pass, that from one new moon to another, and from one sabbath to another, shall all flesh come to worship before me, saith the LORD.
And it shall be, that whoso will not come up of all the families of the earth unto Jerusalem to worship the King, the LORD of hosts, even upon them shall be no rain.
And if the family of Egypt go not up, and come not, that have no rain; there shall be the plague, wherewith the LORD will smite the heathen that come not up to keep the feast of tabernacles.
This shall be the punishment of Egypt, and the punishment of all nations that come not up to keep the feast of tabernacles.
And they shall go forth, and look upon the carcases of the men that have transgressed against me: for their worm shall not die, neither shall their fire be quenched; and they shall be an abhorring unto all flesh.
Why would they be going forth, looking upon the carcases of the men that have transgressed against Him, unless it was a stark reminder and a dire warning, that if you, too, transgress against me, you, too, will end up like these? Would this threat and reminder be in affect for all of eternity though, or just a small portion of it, say a thousand years?
And then we have the following to add, which also appears to transpire during the NHNE.
Isaiah 60:12 For the nation and kingdom that will not serve thee shall perish; yea, those nations shall be utterly wasted.
How can that be fulfilled after the following has already been fulfilled, meaning Revelation 20:7-15? Those in Isaiah 60:12 their fate would be the LOF judgment, obviously, except the LOF judgment would be history and never something that's ever going to happen again once Revelation 20:7-15 fulfilled. What I'm getting at then, if Isaiah 60:12 is meaning during the NHNE, and that the NNE are meaning after Christ returns, then so does Revelation 20:7-15 have to be meaning after Christ returns, in order to fulfill Isaiah 60:12 before the LOF judgments are past history to never happen again for forever.
It seems to me none of the all flesh in Isaiah 66:23 would be including immortal saints though. They would already be before Him worshiping Him, thus wouldn't need to come and do that since they would already be doing that by dwelling where He is dwelling, that being in the NJ.