The old steam gamepad keyboard was also predictable in this way; I don't know if it's still used, I just remember being impressed by the concept. With two sticks and shoulder buttons I think you could really get somewhere with this idea
Steam's keyboard was mentioned in the Gamasutra article linked to in the article[1], which I found more interesting than the original article. I'd recommend reading it; the two-stick entry method detailed by the end of the article makes basically every game-pad entry system I've ever used feel archaic.
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.
It was the Big Picture "Daisy Wheel" keyboard. They've since removed it to focus on what I think is a much weaker controller keyboard designed primarily for the Steam Controller that is pretty garbage for standard xbox controllers.
[1]: https://www.gamasutra.com/blogs/CharlieDeck/20170721/301392/...