I'd love to know too.
It's clear that originally, everybody was supposed to be dead. Whether Marlena was always supposed to be the killer, and what was supposed to happen had everybody stayed dead is a mystery. I guess Corday knows, but if you asked him he'd probably say that what played out on screen was what always was going to happen.
Also, at the time of his first appearance, Luke was still being played by Christopher Tavani, and, therefore, much younger than Karl's character. This was when Will had just been released from prison. Will saved Luke from his bullies at a time when Lily was trying hard to get Will locked up again (as she couldn't forgive him for murdering her sister).
About a year later, Luke has been SORAS-ed (with Jake Weary, then Van Hansis) and started hanging out with Kevin.