Last modified: 2012-09-23 00:09:39 UTC
https://www.mediawiki.org/wiki/TitleKey#Installation tells, that $wgEnableMWSuggest = true; must be set in LocalSettings. Is there a reason (objection) not to move this into the extension ?
wgEnableMWSuggest itself doesn't control much other than loading a legacy module in core. Also, this extension adds a database interface for case-insensitive search. It doesn't directly have anything to do with search suggestions, so enabling that seems inappropriate. And with the pending removal of mwsuggest from core (bug 40448), it would become obsolete. Right now by default (both the download bundle and wmf-deployment) we use the Vector extension's SimpleSeach module which has its own configuration setting.