It would be really nice to control fader, send levels, solo, mute, monitor control, transport and some much used buttons from a touchscreen.
I tried using one with the normal mixer and it was not a pleasurable experience. I'm now looking for a Wacom cintiq and tipro 128 pos keyboard as i think this will be a very fast mixing and editing combination and sufficiently precise for fader and plugin control. (tipro didicated PMX keycaps wink wink

But a dedicated touchscreen especially with remote/wifi capability would be very nice. Controlling monitor mixes at the recording stage having nice touch faders, metering and start/stop recording with big buttons would be a good addition.
You could even think about "personal" mixers on screen for musicians on smartphones or tablets.
Maybe some would like some basic hardware faders to go with this. This could make a hardware mixer obsolete for most mortals. A good source of inspiration could be the Digico S21 system of tiles to arrange channels and busses.