Here are some images of the Lenovo ThinkPad X230T and the Yoga 15. Some things have remained the same while others have changed dramatically.
The X230T is a 12-inch system, the Yoga 15 is a 15.6-inch system. The size differences are obvious, but the design changes and material differences are quite noticeable. You can see the replaceable battery of the X230T sticking out, while the Yoga 15 has an integrated battery. The hinge mechanism of the X230T has been replaced by two hinges that rotate the lid all the way until is in contact with the bottom side of the machine. I prefer the rapid conversion of the X230T, but I also acknowledge the more supportive and hopefully longer lasting hinges of the Yoga 15.
While the Yoga 15 has an Nvidia graphics card it remains thinner than the older generation systems that had no discrete graphics. The ThinkPad Yoga 15 does not have ExpressCard, which can be useful in some cases. (One use is external graphics support via ViDock and other eGPU devices).
The Yoga 15 that I have does not seem to support a digitizer, but if it did it would be the biggest portable tablet to have it. Maybe in the second generation one we will see a digitizer. The X230T does have digitizer input, based on model of course, but the smaller drawing surface can reduce the amount of hand written notes, drawings, and math that is performed. Also, notice the old style VGA on the X230T? New devices are focusing on versions of HDMI and DisplayPort and are discarding the older ports.
The new ThinkPad Yoga systems lay completely flat. The X230T has a slope. Some people like the completely flat design, others prefer the slight slope.