Touchscreens are fundamentally limited by the size of your finger. Firstly because you have to physically press the UI element you want to interact with. Secondly because your finger obscures whatever's underneath.
Of course, you can get around this by decoupling the physical location of the UI element and the physical location of your finger. It's called a trackpad.
Touchscreens are great for some tasks. But they are not great for tasks involving high information densities (writing, spreadsheets, mostly anything that can be classified as "editing"). For those, people will continue to use keyboards and mice until they evolve cone-shaped transparent fingers.
As soon as they start to get over the 11-to-13'' form factor (and lower in price), they're going to replace the current generation of work laptops. They'll get thinner and thinner; as batteries and bluetooth-like technologies improve, sooner or later they'll even lose USB ports, and you'll be left with a device that is literally a screen and a keyboard. Some models will have a detachable tablet screen, no doubt, but the heavy lifting will still be done with a real keyboard.
Take a step back, and really consider how likely it is that laptops are FOREVER. It might be true, but things change and I think it's historically much more likely that ANYTHING you point a finger at today will be transformatively replaced in due time, than it is that you'll be able to accurately predict a permanent future for whatever an ultrabook is.
I actually don't have any idea what an ultrabook is, but it sounds like a very small idea... not something I'd bet on or invest in for the very long term.