As I type on my tab... I think you're right, but I also think it will be a bit in coming as new UI tools/devices/paradigms will need to be more commonplace.
I use a keyboard with my tab as I type now, but I'd NEVER attempt to type this using the onscreen keyboard - it's simply too clunky and slow. Form factor will always play a crucial role, so it will be up to new, innovative software approaches to overcome the limitations of form factor to truly make the new mobile world more productive.
I'm a bit of a bigot when it comes to some mobile technologies though -- I loathe onscreen keyboards that are completely covered by my 2 thumbs, and refuse to use them. So my phone is out. My tab is much better, and I can actually use it for SHORT input.
Voice is currently out of the question as the licensing models for it are prohibitive. i.e. The server/service model makes using it in any kind of software too expensive for anyone except the major corporations that develop or own the software. This is NOT good for consumers - it is a hindrance and it is stopping the advance of mobile technology/software/productivity more than anything.
Were voice to become practical for software authors to use, it would instantly revolutionize computing overnight.
Check out 1 interview Andrew and I did at http://thedocreport.com/
-- it covers some of this.
The next big input will be the "minority report" gestures control, but that is still very far away. Camera sensor technology is more than advanced enough for it. But again, there are proprietary considerations that will exclude it for some time. Also, it really needs a holographic display to interact with, which is again, a fair distance away.
I'm hoping for a tablet/desktop marriage that lets the 2 truly merge as 1 device so I don't have to fart around with syncing and all that BS. It's possible, but it needs some work to get there.
Just imagine plugging your tablet into your desktop, doing video editing, taking the tab off to a client, showing the video, then doing a few minor touchups on the video right in front of them on your tab, delivering the final video right there, then going back, plugging the tab into the desktop and RESUMING the edit to archive it without screwing around with syncing and all that BS.
I really want to see my tab and desktop share all the same resources as a sort of grid computing where the individual nodes can function on their own or together. That would be sexy stuff. Just add more nodes for more power. Yeah, definitely sexy stuff!