Some progress: https://github.com/apache/solr/pull/3829
I think the org.apache.solr.client.solrj package should be used for not only SolrClient (it's there now) but for HttpSolrClient (now that it's abstract & simple), but also CloudSolrClient. It's debatable what belongs in "impl"; I don't love that package name TBH. But the classes in org.apache.solr.client.solrj should be chosen conservatively since we have a rich set of sub-packages to organize most things. Thus *only* the most foundational things that otherwise have no obvious home belong in org.apache.solr.client.solrj.
