suggestion: Ju-on, The Prequel
problably already considered (like "Infernal Affairs" if I'm not mistaken?):
wouldn't it be fun to shoot a "final" instalment to the series in which,
after showing (some fun examples of) the ever worsening "contamination" (in an apocalyptic manner why not),
the film would retrace the first step of the original family, when the future murderer and murdered ones move in the house as an unususpecting happy family?
cf. the idea of possible / impossible entropy: decay in reverse, as explored by "Irreversible" or "5X2". All along the way, the story could/would show how the tragedy could have been averted. ...up until the father finally slaughters the family, thereby ending the saga in a neat return to the start of the first episode.
I thank you, that will be 10.000 for the idea. ;-))