The primary reason for this work would be to reduce duplicative features and effort in supporting both the Elasticsearch Statistics engine AND the Solr Statistics engine. As noted in our Roadmap & Strategic Planning documents, one of the goals of DSpace over the next few years to to reduce duplicative features where such duplication is unnecessary (and provides no significant benefit to our users).
Per discussions in the Developers Meeting on Nov 11, 2015, we are recommending that Elasticsearch Statistics support be deprecated in the upcoming 6.0 release, and removed/replaced in the 7.0 release.
At this time, we have no one who is willing to continue maintenance of the Elasticsearch Statistics codebase. We are aware however that there are features (namely reports / visualizations) that are unique to the Elasticsearch Statistics feature, and we plan to migrate those over to the Solr Statistics engine.
The path towards removal would be as follows:
1. Deprecate Elasticsearch Stats in 6.0
2. Work to migrate unique statistical reports/visualizations from Elasticsearch to the Solr Statistics engine.
3. Provide tooling to migrate Elasticsearch Stats to Solr Stats
4. Remove Elasticsearch Stats in 7.0, in favor of the Solr Stats engine.
Until we can migrate users off of Elasticsearch Stats, we will not remove it entirely. However, once deprecated, we will not provide any additional features/improvements to the Elasticsearch Stats engine (bug fixes may still be provided if/when deemed necessary).