This functionality was added here: https://phabricator.wikimedia.org/T217182 by @RheingoldRiver but later removed (I think accidentally).
The default usage seems very counterintuitive, would it make sense to have this configuration (suppressing replacement of link text on redirects and links) the default and something like: $wgDisplayTitleFollowRedirects = true; required to override this?
Change 938352 had a related patch set uploaded (by Cicalese; author: Cicalese):
[mediawiki/extensions/DisplayTitle@master] Add tests for $wgDisplayTitleFollowRedirects
It isn't clear that this functionality ever went away, but at any rate, it is there now. I added tests that confirm that the behavior is as expected.
As for the default value of the flag, the default behavior of replacing the link text for redirects has been around for quite a while and it isn't clear that the default should change.
Change 938352 merged by jenkins-bot:
[mediawiki/extensions/DisplayTitle@master] Add tests for $wgDisplayTitleFollowRedirects
Change 940436 had a related patch set uploaded (by Cicalese; author: Cicalese):
[mediawiki/extensions/DisplayTitle@REL1_39] Add tests for $wgDisplayTitleFollowRedirects
Change 940437 had a related patch set uploaded (by Cicalese; author: Cicalese):
[mediawiki/extensions/DisplayTitle@REL1_40] Add tests for $wgDisplayTitleFollowRedirects
Change 940436 merged by jenkins-bot:
[mediawiki/extensions/DisplayTitle@REL1_39] Add tests for $wgDisplayTitleFollowRedirects
Change 940437 merged by jenkins-bot:
[mediawiki/extensions/DisplayTitle@REL1_40] Add tests for $wgDisplayTitleFollowRedirects