Nations & Representatives

In Young's Literal Translation, an Old Testament Bible prophecy can say "nations" - but in fulfilment, it can mean representatives of the nations. 

For example, the early Church prayed, quoting an Old Testament prophecy and applying it to their own time, to Jesus:

ACTS 4:25-27
25Who by the mouth of thy servant David hast said, Why did the heathen rage, and the people imagine vain things?

26The kings of the earth stood up, and the rulers were gathered together against the Lord, and against his Christ.

27For of a truth against thy holy child Jesus, whom thou hast anointed, both Herod, and Pontius Pilate, with the Gentiles, and the people of Israel, were gathered together,

Young's Literal Translation of verse 27 says:

27 for gathered together of a truth against Thy holy child Jesus, whom Thou didst anoint, were both Herod and Pontius Pilate, with nations and peoples of Israel,

quoting Psalm 2:1 

"Why have nations tumultuously assembled (YLT)".

So maybe the prophecy about nations keeping the Feast of tabernacles, didn't necessarily mean literally whole populations, but representatives from the nations. 

And we do see examples in the Bible of people from "every nation of those under heaven" in Jerusalem for the Feast (e.g. Acts 2:5).

And if so, then the historical fulfilment of that part of the prophecy may already be in the past.

Placing it in the future seems to conflict with New Testament theology anyway. And isn't necessary given the way the New Testament often divides and interprets Old Testament prophecy. Other physical details in the prophecy also seem to make it awkward to place in the future.

Conclusion: it isn't God's plan for us to carry out the Feast of Tabernacles in future.