I really like the new details page design, is much more user friendly, having the colors and sizes at plain sight is much much better than in a menu. But I have a few suggestions:

1. The text that appears right after the sizes that says something like:
Men's Premium T-Shirt is in stock and ready to be personalized when you order it.
In my case this shouldn't be visible because I have the T-shirt Designer disabled in my store. I guess that you could read the value of this option from your database and if it's enabled show it, and if it's disabled just hide it.

2. As Scott said in a previous comment, the Design details should be right next to the item preview, even before the More products option.

3. I think that the tags are not important for the customer/store visitor, so I think this probably should be hidden.

And finally I just have one question: the pictures that are right after the size chart, can we customize these or decide if we want to show them? Because like they are right now with no design on it, for us that have the T-shirt Designer disabled, I don't think they add much to the store.