The auto-config attribute has been used to pick the best indexing config according to the cache type: it was more useful when Infinispan supported both shared and non-shared indexes.
Since now the only index type supported is non-shared (one local index per cache) and since in Infinispan 12 the entity configuration will be mandatory, the auto-config role is diminished and its changes added to index in Infinispan 11 should become the default on ISPN 12.