It would have to be some completely new technology. Nothing else we have right now can replace a keyboard because it has a very specific function and is very very good at that.
What else do we have and how does it compare to a keyboard?
- replacing a physical keyboard with one pictured on a touchscreen: horrible for typing long text documents. Ergonomic disaster unless you put the screen right where you would have a physical keyboard (flat on your table). Same for similar stuff like those "project a keyboard on your desk with a laser" solutions, This is pretty much "replacing a keyboard with something which is used the same way, but it is just worse at being a keyboard".
- voice input: gets very tiring after a while (anybody who has a job which involves talking all day long knows this). Slower than just typing, especially if you have to correct something when the computer misunderstands you. Formatting text / putting it where you want on the screen (e.g spreadsheets) is difficult. I can only see this as a good solution when you need to input text but your hands are not free (e.g. dictating a text message while driving your car). Also, who wants to work in an office where everybody is talking all the time. That's just annoying - plus there are the obvious privacy problems. Plus technical issues which need to be solved (voice recognition when there are dozens other people talking at the same time).
- using eye tracking / brain wave stuff (electrodes, whatever): too slow, too inaccurate. Also probably tiring. Why track eye movement when we have ten fingers which can just press a button. Also probably only a niche solution for when you cannot use your hands.
- plugging a cable into your brain and just thinking the text: that's just science fiction and probably at least a hundred years away.
The only decent alternative solution is voice recognition, but even that has obvious flaws - the main one being that it is not a good solution for an office setting.