I have to agree, he would be a perfect Light. I saw 17 Again today, and it only further solidified my idea of Zack Efron as Light. Not that I'm counting on it happening, but I really do think he would do the role to perfection.
I honestly think most of the people who have a problem with him, don't actually have a problem with him...they have a problem with his most famous movies - High School Musical. I hate those movies with every fiber of my being, but it won't stop me from seeing the skill he genuinely has as an actor, something I am learning increasingly every day lately.
And yes, Lillard is Shaggy. He's just such a psychotic goofball, I think he would fit the role well.