Two of the oldest interfaces are the abacus and the map and both are still widely used. They have survived because of their simplicity and ability to serve a narrowly defined need. However, Rebecca Rosen at The Atlantic thinks maps will go away. By integrating more and more information into a location (weather, restaurants, gas stations, etc.) the notion of "map" breaksdown replaced by a new interface for "geospatial information".
Of course, the really big question in interface is whether the tablet will replace the keyboard. The keyboard was invented about 170 years ago and was unchallenged until the iPad. Where I now think interface will go is toward combined devices--both a physical keyboard and a touch interface. The advantages of each interface combined outweigh the advantages of either interface. Just need somebody to come up with a design. Maybe a 6 inch Samsung note would be big enough to have a decent keyboard on the horizintal axis.