In the alter universe where Scorpius goes, Voldemort has taken over the world.
Why then is everybody using his name? Even in the original series,
a. Death Eaters call him the Dark Lord
b. They get angry at Harry when he uses the name Voldemort
c. Under the assumption that everything up to the battle of Hogwarts remains more or less the same, they must've kept the taboo still working, since Ron and Hermione were still on the run, and (possibly) other members of the OOtP.
The third thing, I admit is just an assumption (a valid one I think), but what about the others?