Just wanted to throw this out there for discussion. Solr's default query response format is still XML, despite the fact that Solr has supported the JSON response format for over a decade, developer mindshare has clearly shifted toward JSON over the years, and most modern/competing systems also use JSON format now by default.
In fact, Solr's admin UI even explicitly adds wt=json to the request (by default in the UI) to override the default of wt=xml, so Solr's Admin UI effectively has a different default than the API. We have now introduced things like the JSON faceting API, and the new more modern /V2 apis assume JSON for the areas of Solr they cover, so clearly we're moving in the direction of JSON anyway. I'd like propose that we switch the default response writer to JSON (wt=json) instead of XML for Solr 7.0, as this seems to me like the right direction and a good time to make this change with the next major version. Before I create a JIRA and submit a patch, though, I wanted to check here make sure there were no strong objections to changing the default. -Trey Grainger
