I'm converting a system with lower case pages names to wikipedia, and the lowercase is fundamental to the design and backward compatibility. So how I ensure the a link to a fan-bay-deep-shelter page displays the Fan Bay Deep Shelter text I put in the DISPLAYTITLE. I'm happy to edit the extension source code.
Topic on Extension talk:Display Title
It seems that setting
$wgCapitalLinks=false;
as mentioned in https://www.mediawiki.org/wiki/Manual:$wgCapitalLinks gives me the behaviour I want