I don't know anything about this story so cannot comment about them packaging proprietary features. But here's my thought about the trademarks claims from Elastic. The only info I have is the blog post they shared.
Elasticsearch is a name of an open source project. Why is calling something "Amazon Elasticsearch Service" a trademark issue? It's not Amazon's fault they called their company after the name of an open source software (the OSS came first btw). Also, IMHO calling it "Amazon Elasticsearch Service" is fair since it represents exactly what it is. Would it better if they instead took the code, made some closed modifications and then released a service around it with a new name? My thought is no.
The open source project trademarked the name of the project. Because it is trademarked, Amazon requires permission to use the name of the project.
This isn't unusual, many other open source projects trademarked the name of their project. Google has some guidance on why a project might want to do this.
Elasticsearch is a name of an open source project. Why is calling something "Amazon Elasticsearch Service" a trademark issue? It's not Amazon's fault they called their company after the name of an open source software (the OSS came first btw). Also, IMHO calling it "Amazon Elasticsearch Service" is fair since it represents exactly what it is. Would it better if they instead took the code, made some closed modifications and then released a service around it with a new name? My thought is no.