The dark tower has very little to do with dark followers bases, it was a tower in Hogwarts that was added in the third movie as basically a very high tower with a cell on top so Sirius Black could be locked up inside. It lasted for 3 movies until the filmmakers required the astronomy tower in the 6th movie, by which time the tower was replaced by the astronomy tower. For reference, here's a picture of the dark tower I believe LordNic30 is referencing:
On that note, I don't think this will be added. The castle in PW is based on how it was seen in the last 2 Harry Potter movies (and the most recent Fantasic Beasts movie!) with the only obvious alteration being the presence of 2 viaducts rather than one. I don't believe the revelius update will see this tower added, and if it were to be added afterwards, I don't think this tower would fit very well or add very much to the castle as it exists now. But that's just my opinion