Obviously the new prefab system is having a lot of problems and people are concerned right now. Two big general issues: 1) Backward compatibility. I wasn't able to convert any existing project to the new prefab system in the 2017.2 special build (and still the same case with the 2018.3 beta build). A lot of it were due to editor-crashing bugs. New projects work wonderfully ofc. 2) Workflow Overhead. New workflow adds a bit of cognitive overhead on editing simple prefabs. The old prefab system was simple and predictable, albeit more restricted. Both of these problems can be mitigated if the new improved prefab system does not replace the old system, but exists as something standalone. Because Prefabs are such integral part of the engine, I feel that the old system should be preserved as a whole. Otherwise I'm afraid, a lot of people will stay on 2018.2 for quite sometime. I know it's probably too late for Unity to do anything drastic now... but still want to vent this one out.