Thanks for the suggestion! I had not heard of Matterport before, but it would be great to have compatibility with it.
As it stands, I suspect that you could use some Matterport files with Cesium already. You should be able to upload the generated photogrammetry meshes and point clouds straight to Cesium ion, and from there use them with Cesium applications. If you try this, please let me know how it goes.
For 360 photos, I think your best bet would be to look beyond the Cesium plugin. You can add 360 images to Unreal projects using actors like the HDRI Backdrop. There may already be a tool to link up Google Street View to this actor.
If I got anything wrong about how Matterport works, please correct me. If it’s not compatible with Cesium at all, that would be helpful to know so we can possibly support it in the future.