To support Elastic Common Schema, some of the fields would have to be renamed and some possibly added to Elasticsearch JSON logs.
There is a project containing a log4j2 layout that can be used to make this task easier. https://github.com/elastic/java-ecs-logging

Also since this would require new fields being added, we should consider making it easier to add more fields in the future to support "special log events" that would make monitoring of Elasticsearch easier. Example would be a special log event when cluster state changes. Draft was done here #44336