With the release of Elasticsearch 2.0.0-beta1, the Delete by Query API has been transitioned from a core feature to a plugin due to significant issues with its previous implementation that included unexpected visibility of deletes, segment explosion, merge storms, and risks of data corruption due to inconsistent replicas. The new plugin addresses these problems by using a safer method involving scan and scroll requests to find document IDs before deleting them via the bulk indexing API, although this method is slower. The decision to shift to a plugin was made to maintain a reliable and minimal core, as the previous Delete by Query feature, despite its speed and popularity, posed risks that couldn't be ignored. Additionally, deleting a type's mappings has been removed due to potential index corruption risks, encouraging users to adopt alternative strategies such as using separate indices.