Ah Sir David MacKay. I so respect him. Great explainer and speaker. He had built this text entry tool called Dasher [0] - that I'd heard him introduce at Princeton around 2006. It was basically an early language model that predicted which characters are more likely than others, given what you've already types and it would adjust the sizes of the available next characters based on their probabilities.
[0] https://dasher.at/about/