VRSpace.org

Mozilla made authoring tool for hubs already: https://hubs.mozilla.com/spoke
Exporter seems to be in Editor.js starting around line 340 https://github.com/mozilla/Spoke/blob/master/src/editor/Editor.js
And it seems to export GLTF:

 const exporter = new GLTFExporter({
      mode: "glb",
      onlyVisible: false,
      includeCustomExtensions: true,
      animations
    });

See how it can be integrated into VRSpace.