With the end of the Google Earth plugin and no sign from Google to open up their new WebGL renderer, GEFS was doomed.
CesiumJS was considered the best alternative and after some testing became a viable replacement.
Cesium is backed by an active community and has a bright future.
GEFS was quickly migrated in order to beat the end of the plugin, so some things may still have to be improved. Details on the migration to be found here.
I would be glad if you could report bugs and problems in a constructive manner on the bug report forum
I will keep working on finalizing the migration and hopefully keeping on improving GEFS.