If it's Toho that's making it and it's a more Japanese-specific production, then I can understand going with Diamond is Unbreakable. It's a more centralized location and with a more Japanese cast. Doing Stardust Crusaders would probably be pretty costly what with the world traveling, along with requiring more to trim and edit.Huh. They're gonna do Diamond is Forever and not Stardust Crusaders?
Now, if it were a more Western production, then I think Phantom Blood would have been a good choice to adapt.