Agreed, it's just a concept at the moment, but it has a solid enough base in UI research to warrant discussion.
Seriously, our angular precision with our fingers is hellaciously better than our linear. No idea why. Oughtta take advantage of that, y'know?
And let's say that 26 *is* too many. What's the sweet spot? The 10 of the digits? 15? Do we shunt Q, Z, etc off to a subwheel-of-the-lesser-used? (ie, minimalist predictive input) Do we have the ring change according to the previous letter, but never exceed the max number of elements? (ie, true predictive input) All sorts of possibilities.
The question is... are any of these better than having a slide-out tiny QWERTY keyboard?
I see an advantage over the QWERTY because it's usable with one hand, for instance.