why does the playwright stop short of naming what the dead are waiting for

The playwright, through the voice of the Stage Manager, says that they are waiting for the "eternal part of them to come out clear." He does not use the word "soul" which is one possibility of that "eternal part" which he could be referring to. He certainly emphasizes that they are waiting for something to happen, which would indicate another reason why he does not name what they are "waiting for" - like the characters in the play, the reader must wait to see what is going to work out in the play at its conclusion.