I DOUBT Nathan will be in this show. It will be an expensive show without having to pay Nathan his usual star salary. The show will be a hit without a bonafide star such as Nathan. I would guess that they would bring another musical theatre veteran (someone like Denis O'Hare) to do the role. If this show is indeed a hit-in-the-making as people are saying, the show won't need a star to be a hit.
As for Matthew Morrison, he might be busy with Tarzan when this show previews and Michael Arden might be busy too doing the Dylan musical. Ideally I think Michael Arden would be perfect for the role, but the producers will probably think that hetero Matthew Morrison might be more believable as a womanizer.
I am crossing my fingers that this show will debut in San Diego...
"It does what a musical is supposed to do; it takes you to another world. And it gives you a little tune to carry in your head. Something to take you away from the dreary horrors of the real world. A little something for when you're feeling blue. You know?"