Ecumenism is, by definition, interdenominational.
It is important to remember that the Body of Christ is interdenominational.
We may choose labels for ourselves and others—and such labels have their place—but Jesus never assigned denominational tags. He said,
“All those the Father gives me will come to me, and whoever comes to me I will never drive away” (John 6:37).
The Body of Christ is made up of “everyone who calls upon the name of the Lord” (Acts 2:21), and the gospel of salvation by grace through faith unites believers, despite our differences.
Heaven will forever be interdenominational, as “every nation, tribe, and tongue” (Revelation 5:9) will worship the same Lord in harmony together forever.
The Metropolitan Platon Gorodetsky (1803-1891) of Kiev had a saying that 'the walls of separation do not rise as far as heaven'.