1.) His new model looks so much better than the old one.
2.) His ears are now pointy like older Xehanort's.
As for the first point, I'm so glad that they kept working on the model. It was so cringey at first, but now it's looking quite nice. I had expected them to work on it to some degree, but I was more hopeful than anything. Now we have something that looks like a proper next gen model for the guy.
As for the second point, it can't be a mistake - Young Xehanort has always had rounded ears, while older Xehanort has always had pointy ears. The pointed ears are so intrinsic to Xehanort's nature that when he places his heart in others, they begin to develop the same pointed ears - and yet his younger self doesn't have them. This means that at some point in Xehanort's life, something produced this trait within him.
... yes, I believe that the Xehanort we see there has obtained the keyblade No Name and thus has developed the pointed ears because of it. Young Xehanort even speaks as if he's continuing Luxu's mission there. "I have more to observe."