Looks like it should work fine:

1. If the text can be treated as a title, use it verbatim.
2. Otherwise, pull the titles from the links table

$dp = Title::newFromText($dMsgText);
if( $dp ) {
if($dp->getNamespace() != NS_TEMPLATE) {

1. FIXME we assume the disambiguation message is a template but
2. the page can potentially be from another namespace :/

		wfDebug("Mediawiki:disambiguationspage message does not refer to a template!\n");

}
$linkBatch->addObj( $dp );
} else {

1. Get all the templates linked from the Mediawiki:Disambiguationspage

[snip]
}

IMO this is pretty awkward -- requires no brackets for a single item, *or* brackets around multiple items -- but it'll work. In fact, it would *fail* to work if the requested change were made, since on a default install the page wouldn't be recorded in the database until it was customized, so the check for live templatelinks would fail to recover anything.

(Well on my wikis, instead of hoping folks can make heads or tails of
what is meant, I just chuck 'Disambiguations' into my LocalSettings.php's

function JidanniLessSpecialPages(&$list){
foreach(array('Uncategorizedimages','Unusedimages','Withoutinterwiki','Upload',
'Newimages','Listfiles','MIMEsearch','FileDuplicateSearch','Filepath','Booksources','Mostimages','Tags','Disambiguations'

	      )as $i){unset($list[$i]);}global $wgUser;if(!$wgUser->isAllowed('editinterface')){unset($list[Ipblocklist]);}

return true;}$wgHooks['SpecialPage_initList'][]='JidanniLessSpecialPages';

and poof, it's gone.)

This works for me in current HEAD, and if it didn't work in 1.16, that'd be obsolete by now.