[kijin]

You just make another couple of custom UIs for "in-between" cases.

Notebooks with a touchscreen can be treated either as tablets with a bunch of integrated USB/Bluetooth peripherals, if you want to use them like MS Surface, or alternatively, a regular notebook with an oversized multitouch-enabled trackpad that happens to be the display. So there's no need for a new UI paradigm there.

Super-large or gesture-controlled devices will probably need their own UI paradigms when they become mainstream.

None of this is meant to imply that every device will need its own, incompatible, radically different UI. Competent designers should be able to come up with a "line-up" of 3-4 UIs that "gracefully degrade" into one another, e.g. a menu bar appears if the device has a mouse, and non-maximized apps are allowed if the screen is larger than X inches. And of course, lots of options for power users, e.g. I want non-maxed apps in my 7-inch device even though the default only triggers them in 10-inch devices, and I want Alt+Tab to switch between windows rather than apps.