3 Dimensional screens
The interface which is one of the big reasons keeping people from linux (although not recognized for that by many people) will be replaced by a 3D interface in the future. There is already technology making it possible to show 3 dimensional images without goggles, the only problem is you have to be right in front of these screens. Using a personal device like a umpc your in front of the screen already, so if the technology becomes cheap enough and someone builds a usable interface, it will probably find wide adoption quickly.
The great thing is that with Linux it's easy to create a different interface, because that's not an integral part of the OS.