Glad to see this thread bumped because, I gotta say, this has been one of the worst Unity decisions that has impacted my dev flow significantly. In order to "properly" use Entities and keep up to date, you have to sacrifice all stability across Unity (and LTS support) for a preview package and workflow. Unity has basically forced an "all or nothing" approach to preview packages with this move. It's a serious struggle and blocker for devs who want to ship something production ready for everything non-entities. There were so many fixes and improvements going into Entities 0.12 through 0.15 that do not have dependencies on Unity 2020. So everyone who invested time into Unity 2019 LTS is left drowning in outstanding issues with no support. Everything from corrupted heaps and broken APIs to huge performance issues. I've forked my own version of 0.11 and I'm manually integrating over fixes from Unity in later versions, such a bizarre thing to make us do. If there was any indication of this happening earlier, rather than so abruptly, would have never invested time into Entities at all.