I have some sympathy for Elastic, but I just do not agree that AWS is doing anything wrong or against the spirit of open source. When they run into things that need to be fixed or improved in the projects they upstream them. The majority of work AWS does is in "operationalizing" the project for their cloud. It might be cool and interesting if they let us see how they do this but it is not like that work directly translates back to the open source project. Anyone that has worked with Google open-source stuff has run into the same issues where there is some behind the scenes magic that Google has internally that the projects can leverage to make them scale better etc.
It is Elastic's right to change the license if they so choose. If they own trademarks that they believe are violated it is up to them to take those challenges to a court and seek damages. Elastic is trying to have it all ways though. They want you to believe the new license is open source .. sort of true but not really. They want you to believe AWS has done something wrong. This I do not buy at all. What is special about Elasticsearch? The entire Internet and the Cloud is running on all kinds of open source software up and down the stack. It is in the interests of the behemoths that run these stacks to upstream fixes and improvements and generally they do. That does not mean they have to contribute the proprietary wrappers they have put in place around them as part of building their business model.
AWS needs to be focused on its customers, not companies like Elastic and Mongo. If its customers would prefer to operate an Elasticsearch service provided by AWS as opposed to Elastic, then that is a problem for Elastic to resolve.