I see what you are saying there but that is not the same as what it is now.
When you read 'nations' there it is clearer if you think 'peoples'.
1484. ethnos - nation, gentile, people
1471. goy - nation, gentile, people
This you have right:
It suggests a diversity of peoples and governance under Christ's rule.
The key being the second part of that, 'governance under Christ's rule.'
Today we have different 'nations' (countries) with their own borders, laws, governance, languages.
Under God's kingdom and governance under Jesus' rule, there will be 'peoples' of all the current 'nations', so a 'diversity of peoples' you seek will be there, but the culture, history, and languages are done away with and start anew under however/whatever God has instore for his 'peoples' living under kingdom rule.
[21And I saw a new heaven and a new earth; for the former heaven and the former earth had passed away,5 And the One seated on the throne said: “Look! I am making all things new.”]
[11 Since all these things are to be dissolved in this way, consider what sort of people you ought to be in holy acts of conduct and deeds of godly devotion, 13 But there are new heavens and a new earth that we are awaiting according to his promise, and in these righteousness is to dwell.]
[17 For look! I am creating new heavens and a new earth; And the former things will not be called to mind, Nor will they come up into the heart.]
[ 9 For then I will change the language of the peoples to a pure language, So that all of them may call on the name of Jehovah, To serve him shoulder to shoulder.’]