You are on to something!
First of all, somewhere in all the multi-touch Apple patents they discuss:
1) tactile feedback where the surface gives a small vibration when/where touched.
2) the ability to detect pressure (ala a paintbrush) and attack (ala a piano KB)
This gives the MT an advantage over traditional KBs.
Also, a MT device can be in addition to the display device(s) attached to the computer.
The MT is an empty slate and can assume whatever format is useful (to provide input/output) for the application running at that time:
-- Equalizer KB with slider controls for AV DJ
-- Piano KB (maybe larger or multiple MT devices)
-- An input device for other instruments such as guitar, clarinet and some that aren't even invented yet. (you saw Steve flick the contact list-- imagine playing a rasquedo on a MT guitar).
-- A small, portable, inexpensive MT device that is the (truly) universal remote control-- offering buttons, scrollwheels, sliders, squeezers... whatever? (a quick lookup of universal remotes shows offerings from $129 to $499. mmm... maybe universal remote is the hidden iPhone app
-- a light table for photographer, artist, draftsman, stained-glass designer... cha, cha, cha.
-- a universal game board for Monopoly, Risk, Backgammon, Go...
-- all sorts of medical/forensic applications
-- a gameboy type of portable game (whoops... another button on the iPhone).
-- a universal game input device (ahh... motion sensors on the iPhone)
-- training device for pilots, doctors, auto mechanics...
-- universal/customizable kiosks
This just scratches the surface (heh, heh)... but with MT we have an input (and output) device that can be tailored to the requirements of the application, while, at the same time, personalized to the needs/desires of the user.
With that perspective, the qwerty KB is so 20th (er 19th, 18th, 17th, 16th) century.
I suspect the traditional KB will be around for a while (for us older folks) but the younger generation will be raised on MT devices.