There is no evidence in neither the Quran or Hadith to support this position. I used to hold this position because it was a common view because no one really understood it.
Even Ibn Taymiyyah and his students thought the Mongols were Gog/Magog, you had Indian scholars like Iqbal and a few others whom believed they had been released and the hadith supports this if you read my posts I have touched upon this.
I have yet to to read a refutation, the 999 out of 1000 being Gog/Magog doesn't make sense if you take it literally, we know Christians/Pagans/Jews will go to hell including Munafiq Muslims and sinners not forgiven by Allah including likely those who abandon prayers, it makes no sense that all 999 will be Gog/Magog
"Allah divided mankind into ten parts. Nine tenths constitute Ya'juj and Ma'juj while the remaining one tenth constitutes the rest of mankind."
"They will pass by a river and drink from it, until they leave nothing behind, and the last of them will follow in their footsteps and one of them will say: ‘There was once water in this place.’ They will prevail over the earth, then their leader will say: ‘These are the people of the earth, and we have finished them off. Now let us fight the people of heaven!’ Then one of them will throw his spear towards the sky, and it will come back down smeared with blood. And they will say: ‘We have killed the people of heaven.’ While they are like that, Allah will send a worm like the worm that is found in the noses of sheep, which will penetrate their necks and they will die like locusts, one on top of another. In the morning the Muslims will not hear any sound from them, and they will say: ‘Who will sell his soul for the sake of Allah and see what they are doing?’ A man will go down, having prepared himself to be killed by them, and he will find them dead, so he will call out to them: ‘Be of good cheer, for your enemy is dead!’ Then the people will come out and let their flocks loose, but they will not have anything to graze on except their flesh, and they will become very fat as if they were grazing on the best vegetation they ever found.'”
From these ahadeeth is shows that:
1) They are far more numerous than the rest of mankind, only Allah knows how.
2) Their numbers will be so much that they'll turn rivers dry when they drink from it.
3) When Allah kills them all, the animals will have nowhere to graze on except their flesh showing that their numbers aren't a symbolic or metaphorical.
4) These people are primitive people, they were described as not even being able to speak properly and the idea that they built this technologically advanced civiliation we are living in is just ludicrous.
Also, many of the minor signs haven't even passed yet (such as Arabia turning green) and the appearance of Ya'juj & Ma'juj is a major sign that will certainly not be doubted.