I recently learned that you can type "GK4" into Sydney and it well tell you about ghosts. So apparently there was supposed to be a "Gabriel Knight 4" about ghosts. I guess it wasn't made because Sierra went downhill. I wonder if it ever will be made.

I could be mistaken but I thought that Jane Jensen + some others had a GK4 page up for quite some time and were working on it conceptually but there was never enough interest from outside parties (fans included) and so they recently dropped / gave up on the project.

That sucks. Not terribly surprising considering we're talking about a 20+-year-old series of games that wasn't enjoying "King's Quest" popularity even when it began, but that still sucks.

Maybe there will be a fan-made GK game or a fanmade game loosely based on the concept? There are fan-made King's Quest, Space Quest, and Quest For Glory games so it can happen.