I can name a few games off the top of my head, that are apparently in development but have had no news on for years and it seems that they will never see the light of day.
Duke Nukem Forever. More like Duke Nukem Never.
Half Life 2: Episode Three. As Gabe would say, “No comment”.
Elder Scrolls V. TBH, I found the first one a bit boring, walking for ages.
Can you think of any games that follow a similar trend?