There've been some worries expressed on the changeset comments, namely:
* changing the JSON OpenSearch behavior changes MediaWiki's search box suggestion behavior, and right now it may be unclear just what's going on
a) do this change, but also change the search suggestion module that uses the JSON OpenSearch to use the old behavior
b) do a similar change that switches the XML default to the old JSON default instead
c) cancel this changeset and go improve the search dropdown frontend before tweaking this again?