Did you see the Microsoft Surface? The one I used did this.
I would love if one of these companies that makes 2-in-1 laptops that have detachable keyboards would make one that works when the keyboard is detached. If a good portion of your time with your laptop is working at a desk, you may want to arrange it in a way that is more ergonomic (perhaps, having a higher mount for the screen while the keyboard stays on the desk). Then, when you are ready to go work elsewhere, you reattach and you are on your way. Are there any 2-in-1's out there that do this? If not, has there been any discussion about future ones offering this? Thoughts?