It’s 2019 and I’m wondering this too right now, as TwinMotion is available and I’m not using Revit or ArchiCad, the dynamic link plugins are supposed to give access to FBX and material export options, but the option I have is for BIM Motion export, images, and video’s only, the BIM Motion data exports as 2 PAK files with the base UE4 structure, and the TM and other files don’t import into UE4. My guess is that’s where the files that need to be imported back into the engine are to work with them, unless a plugin is created or the importer in UE4 updated to include that format or an update to the Datasmith Plugin, unless there’s another official way to do it. I remember when old pak files used to just be zip files with the extension changed from *.zip to *.pak without any encryption at all, also how the wav and mp3 files were stored etc… Then again compression for that wasn’t used beyond the built in file format’s compression via the codec’s, more of a thing to organize the file structure, later versions of Windows came out and the zip files were treated more like direct folders you can double click on to view things inside.