The migration toward CesiumJS as a replacement of the dying Google Earth plugin is almost complete. Except for some minor tweaks (smoke effects, clouds), I consider the migration to be successful. The application seems to be stable enough and performance is satisfying.
I just upgraded Cesium to version 1.18 which claims a memory usage gain in Chrome. I also tweaked caching in order to prevent the constant reloading of texture tiles when quickly changing camera direction.
Finally, GEFS is now featured on Cesium's official demo page http://cesiumjs.org/demos.html