That's really interesting! The new steam controller keyboard takes advantage of the dual touchpads to give you the split hunt and peck as described in the study. You can see how there are larger targets for certain letters, and more total inputs that can be picked. However, you have to look at the keyboard to type, it's not a solution for the touch typing problem.
Having experience with precise angles on a gamecube controller in Super Smash Bros Melee, I can't help but feel like I would prefer the penultimate solution in the article you linked, with appropriate zones that can be targeted directly. Locking you to a quadrant and forcing most letters to be a compound input doesn't seem worth it to me. You could also definitely improve the quadrant system by allowing you to break into a new quadrant without returning to the center, maybe by passing the vertical or horizontal center line, depending on the quadrant. But, I obviously haven't tried it myself.
https://i.stack.imgur.com/XDNKX.png
Having experience with precise angles on a gamecube controller in Super Smash Bros Melee, I can't help but feel like I would prefer the penultimate solution in the article you linked, with appropriate zones that can be targeted directly. Locking you to a quadrant and forcing most letters to be a compound input doesn't seem worth it to me. You could also definitely improve the quadrant system by allowing you to break into a new quadrant without returning to the center, maybe by passing the vertical or horizontal center line, depending on the quadrant. But, I obviously haven't tried it myself.