LAS VEGAS—Last year's Lenovo ThinkPad X1 Carbon was a return to form for Lenovo's X1 Ultrabook, with a keyboard to die for, strong performance, and a 14-inch screen in a 13-inch package. This year, Lenovo is taking the X1 branding—light, powerful, high-end machines—and diversifying it. No longer just a laptop, the company is launching a Yoga-brand 360-degree hinge X1 laptop, an X1 tablet, an...