I've tried exporting from both Reality Capture and Agisoft PhotoScan.
For photogrammetry models that have been geo-referenced in the photogrammetry software I can either export in a local, Geographic (WSG84), or Projected (UTM) coordinate systems.
With the exception of the local coordinate system, neither the projected or geographic coordinate systems will process in Cesium ion.
Yes, it would be nice to not have to fiddle with 'placing' the mesh in the Cesium ion UI.