Albert Barnes on Revelation 21:22

And I saw no temple therein. No structure reared expressly for the worship of God; no particular place where he was adored. It was all temple--nothing but a temple. It was not like Jerusalem, where there was but one house reared expressly for Divine worship, and to which the inhabitants repaired to praise God; it was all one great temple reared in honour of his name, and where worship ascended from every part of it. With this explanation, this passage harmonizes with what is said in Rev 2:12, 7:15.

For the Lord God Almighty and the Lamb are the temple of it. They are present in all parts of it in their glory; they fill it with light; and the splendour of their presence may be said to be the temple. The idea here is, that it would be a holy world--all holy. No particular portion would be set apart for purposes of public worship, but in all places God would be adored, and every portion of it devoted to the purposes of religion.