There are Dvorak layouts designed for those using either the left hand only, or the right hand only - for whatever reason.
You say that ‘interlacing’ isn’t the right approach. That’s your opinion. Having typed hunt-and-peck for thirty-some years on a QWERTY layout and then having learnt to touch-type on a Dvorak (two-handed) layout, I would have to disagree with you, and can only suggest “don’t knock it till you’ve tried it.”
I, for one, have always wanted to try a keyboard I saw once (but cannot find anywhere online):
It was basically a cylinder with four buttons on each side. The key was to press all the keys of the binary value of the character you wanted (i.e. if you wanted to make a space you pressed all the keys at once to register a 255). It seems like it would be clunky as hell to learn but a really great, fast keyboards afterwards (except for gaming which often requires multiple key input at once of course).
I was thinking about that, but I think you wouldn’t be able to go really fast on it. It sure would be ergonomic, not having to move your fingers at all. The error rate would also probably be better. It’s a strong concept, but I think it won’t beat qwerty on pure speed. In any case, I think if you go for a radical design, a predictive keyboard would beat anything. With two letters per key and a special (not alphabetic) arrangement, there would be very few word collisions. You would hardly have to ever leave the home row.
But as for the real input method of the future… that’s shapewriting.
That got me thinking for some time. You know, I tried that same test, and I was surprised to feel the same way: “air-typing” feels faster than spelling.
BUT, I have been interested in ergonomics for a long time, and this made me remember something about subjective vs. objective time. Turns out that people is notoriously bad estimating their own performance. A typical case is how switching from keyboard to mouse feels much slower than using keyboard shortcuts or cursor keys; though if you care to record your interactions and actually time them, you will see that the mouse is actually much faster.
You can read a bit about that here:
http://www.asktog.com/TOI/toi06KeyboardVMouse1.html
http://www.asktog.com/SunWorldColumns/S02KeyboardVMouse3.html
So what exactly does that have to do with spelling vs. air-typing? Well… that we should use a timer! 
I will, as soon as I find another touch-typer.
Sounds to me like a “chording keyboard”. The frogpad (www.frogpad.com) is one of them.
(That “binary value” part sounds nasty to me, though)
That’s very interesting. Haha, I love how your links are from 20 years ago… on a Mac… using a one-button mouse… on an SVGA monitor (which is easier to use a mouse with than a high res). Yet the discussion is still very much relevant.
And I think the point of all this, something I’ve been thinking about a lot more than keyboard layouts through the years: is that THE MOUSE SUCKS. It’s ineffably unpleasant to use to the point where, as your source claims, people keep turning to the keyboard even though it’s slower.
In the beginning I used ordinary mice. Then I was dead-set on trackballs, but eventually gave them up. I’ve owned a tablet PCs. I’ve fiddled with he acceleration settings endlessly. Half a year ago I finally got an expensive laser mouse, a quality mousepad, and even teflon stickies. It made a big difference. Yet I still wish that pointing-and-clicking could be as stress-free as looking at a spot and having the computer read your brain (or eyes). I really thought a Tablet PC would come close, but then i found that the spot you touch the pen isn’t quite the same as the spot that gets clicked. This drove me insane.
Why does using the mouse seem to be so vaguely, irrationally unpleasant? Anyone have tips on making it all better?
On the other hand (heh), we now use optical or laser mice much more sophisticated than what was available then; and we have had a number of years to get used to them… to the point that we take them for granted.
Note that Tognazzini does not say that people “turn to keyboards although they are slower”! It’s kind of the opposite: they do because they mistakenly think it is faster.
It boils down to: the keyboard demands more of your attention, so you don’t notice you’re wasting more time. The mouse is more natural, so you keep your train of thought - so you can even be aware of the time needed for your actions.
Sigh.
I am going to sound like a zealot, but… so be it. Mac-head mode ON.
From your description, sounds like you are / have been too centered in the mouse / whatever. That is the problem, you should not be thinking about that.
But, to accomplish that, you need a system that allows you to forget about such details.
I came to the Macintosh after having been a, say, power user in the PC world. That was in 1995 (yes, that Windows was the proverbial straw). Since then I have been using Windows for bussiness and Macs for (geekish) pleasure.
And I can say that with the Mac you could really forget the computer. Meanwhile, Windows always manages to “get you out of the trance”. Always there is a stupid little quirk that, ever so slightly, makes you stop you and realize you are using a so limited, clumsy interface, and that you should have finished already whatever you are doing and why is this taking so long.
Cheesy and prototypical, I know, but it’s kind of like going for a walk to some beautiful place and enduring all the way a little pebble in your shoe. Yes, you can stand it, and theoretically there’s not that much of a difference. …but the experience has been ruined. You won’t remember the beautiful views, but a somewhat longish walk and how glad you were when you reached the end.
As a little disclaimer to ease that zealotry: the “golden age” of the user interface in the Macintosh was before OS X. I lived that between 1996 - 2001, more or less. Now, OS X is still better than Windows IMO, but it’s no longer what it was.
Back then, technically the Mac OS was a decaying piece of junk saved by the grace of its top class GUI. Now, OS X only has a relatively good GUI that complements / is complemented by a relatively good plumbing.
No, I disagree with his hypothesis that it’s because the mouse is so easy to use, people think it’s slower. If the mouse was so effortless to use, people would not notice it. But it isn’t. E.g., take sports. I only really play one sport, handball, but my muscles have developed a memory for it. If I see a handball flying toward me, I can stick out my hand not thinking, and by magic it will end up in the correct spacial location and hit the ball. It takes no thought and I have a fun time playing. But with the mouse, it never gets to that point. Somehow, I can’t just see a button and let my muscles move to it on their own like they should.* There’s always a lot of hand-eye tracking, coordination, correction that never goes away. That is what weighs down the head, making the mouse seem slow. Touchtyping on the keyboard relies on muscle memory well, and despite the task of remembering which key to push, not having to micro-manage your muscles is less strenuous in the end (and hence seems faster).
*Err, not quite. Having disabled acceleration, having decreased mouse velocity, having gotten good equipment, I think i’ve gotten a lot closer to that. But still, I can’t point at something as thoughtlessly and reflexively with the cursor as I can take my finger and press it to the screen.
Tognazzini does not say that people think the mouse is slower because it’s easy to use, but because they feel the keyboard is faster.
Don’t know about your particular problem with the mouse, but… you mention “micro-managing muscles” (which sounds like problems with speed / acceleration) and “disabled acceleration” (which, as far as I know, is usually only to be used with graphic tablets). Are you sure you shouldn’t be using some other acceleration curve? For the record, that’s exactly one of the things that Apple screwed up when switching from OS 9 to OS X… (and there is no official way to set it!).
Another typical problem that gets translated into continuous over-shooting and under-shooting of the mouse cursor is the use of different acceleration curves in different computers/OS/mouse drivers. Do you consistently use the same computer equipment?
If you have to switch computers/OS/mouses from time to time, perhaps you just don’t get to the point where you would get used to some acceleration curve.
Just a thought.