Adapting it to an American cultural context would mean a few things:
- "He seemed like such a nice boy with a bright future ahead of him." This is what we say of school shooters. When they don't look like social maladjusts in a visually obvious way (like that bowl-cut thing a certain recent mass murderer had), they look like ordinary
teenagers. He's not the well-scrubbed, upper-crust Light that would be produced in Japanese or British society (a British adaptation would be slick and socially cutting, BTW). He's in America, where we feign ignorance of class divisions and are taught a higher emphasis on individual responsibility for actions(something that will make the question of Light's motives a little blander).
- This is L:
I've only seen him impersonating Snoop Dogg in Straight Outta Compton, but he's been an up-and-comer in middlebrow arthouse movies for years. I hear he's really good in Short Term 12 and Atlanta. Perhaps there'll be a racial rather than classist implication in Light's choice of victims?
- In the reboot live-action series from a couple years ago, Light doesn't jump right into using the Death Note. Ryuk edges him into it a bit. It's probably an easier angle to take the beginning from than the original.
I think a feature film length version can work fine. There are implications in the manga and anime about the world's reaction to Kira, but not a lot of aspects of society are shown changing from it. From day one, Death Note has been more about plot mechanics, mind games, reversed expectations. You can do that just fine with a pared-down pool of characters (please no Near or Mello) and a plot arc that will probably have the ending of the live-action movie from about 10 years ago. It'd be great if it ended with the midpoint of the anime instead, but that's more just my personal bias.