You can download the latest Power BI connector (and all other next-gen connectors) from here.
Install next-gen Revit connector and publish via that.
Depends on what you are looking for. If you publish your federated model directly from Revit, Power BI 3D Visual already supports it. But if what you are looking for is visualizing multiple Speckle models in one 3D Visual, that’s not supported yet. We are actively working on this.