Its being made. Not much info out there
"Yes, we bought the right to develop StS4 and to release it worldwide. We also have options to develop more sequels for PC and consoles.
The game will be completly in 3D, but without any action parts. StS4 will be a classical adventure like Simon 1+2 or Monkey Island. Mike Woodroffe will give input regarding the story and will be informed about the whole development process. The release of StS4 will be in Q3 06.
More details including some graphics will follow soon."
Heres the link to the website of the devs. Same people who are making The Fall.