In the body comparison shots by Luka you can see that the length (and perhaps even girth) of the neck is different, especially when seen from the back. The shoulder slope is also slightly different. I think the new neck is rather cylindrical and doesn't get wider the more it approaches the collar and shoulders, which the DX10 body does. That might account for at least part of the visible difference.
Here's hoping. Can't wait to check it out in person, it'd be nice to know they recognised that abominable DX10 neck for what it was.