How would the mood of the story change in Vonnegut had made the characters less familiar and more "futuristic"?

Using a futuristic format might have allowed Vonnegut the ability of making his characters a little less real, but I don't believe his intention was science fiction. The mood of the story would most certainly have changed had he gone that route; his characters would probably have been less realistic and more robotic, but the effect would have been ruined.

The mood changes.