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
Possibilities are:
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?