Only recently have Google's and Apple's TTS come close to matching it. Occasionally I still miss T9 like when in a movie theater where I can't speak to type and don't want to look at my screen.
I like being able to type while walking and without looking, and by far the best phone keyboard for that is 8pen [0]. A masterclass in innovative UX imo, and clearly a ton of work went into it. Unfortunately, they pulled it from the play store (and deleted all the tweets on their twitter) some years ago for reasons unknown to me.
Related is MessageEase [1], which is not as good but still passable. But it's incredibly ugly and takes up a ton of space on my screen, so I don't like to use it.
[0]: http://www.8pen.com/
Even if you aren't looking at the phone. You're still distracted as you're thinking about typing. As well has having your hand occupied.
Also, why would you want to be texting in a movie theater anyway?
https://lh3.googleusercontent.com/proxy/ACAiL9UXh-hN-rMMc5J5...
[1]: https://www.gamasutra.com/blogs/CharlieDeck/20170721/301392/...
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.
But if you want others to use it, remember that they are different than you and even learning such a system is a big investment for many people.
Qwerty keyboards work because people can see the keys and they're everywhere. When you come across a keyboard of another layout, even just alphabetical, it's a big pain.
If people are going back and forth from your layout to any other kind, it's going to be a huge headache. And if they put down your layout for more than a couple weeks, they're going to have to re-learn it. Having it be predictable is a lot more desirable if there's ever a time you have to re-learn it.
Phone typing was easy to learn because the letters were both predictable (alphabetical) and because you could look at the letters when you forgot, especially while learning.
Since looking at the keys isn't possible here, I think it's even more important that being able to predict the locations of letters is possible and easy.