When asked about the future of interfaces, Donald Norman points towards the command line, as an interesting metaphor:

"What is to replace the GUI? Ah yes, journalists are constantly asking me that question, hoping I will speak of virtual reality implants by which we fly effortlessly through hyperspaces, finding just the items of interest, then immediately packaging and caressing them to do our bidding in reports, diagrams, and instant insights of wisdom. Well, the answer is much simpler, and it's already here: search. The real surprise, though, is that search engines have evolved into answer engines, controlled through a modern form of command line interface. (...) Even though these three services are called search engines, they are in fact becoming answer services controlled through their command line interfaces. The control language seems more ad-hoc than systematic, and the language forms are still spotty and idiosyncratic, but it is nevertheless a form of command line interaction (...) GUIs were—and still are—valuable, but they fail to scale to the demands of today's systems. So now command line interfaces are back again, hiding under the name of search. Now you see them, now you don't. Now you see them again. And they will get better and better with time"

The main reason he mentions for that is flexibility ("They are tolerant of variations, robust, and exhibit slight touches of natural language flexibility"). Why do I blog this? interesting arguments here, this connects to my interest in the past about chatbots/IM interface as a way to interact with objects.