Thanks for such details, and I like your train of thought. One of the logical reason why calculator layout was arranged the way it is (even today) is because the mechanical calculators prior to digital ones had number 0 to 9 arranged from bottom to top (as shown in the image in my article). That said, both the push button layout and calculators were designed for analog buttons. So when we moved to digital interfaces and especially touch screen phones, there should have been some kind of study done to analyse, does it makes sense to continue using old mode of interface, or there is a need to design new interface for new paradigm (Just how Bell Systems questioned it when the modality changed).

Left to right and top to bottom does make logical sense, but is 3x3 the best possible solution? Even if it is, should we not reconsider placing those buttons in a more easy to reach position without compromising the muscle memory that users have developed using this old layout?

The experiment so far is showing that it is possible, but I would wait and watch where it goes :)

Thanks for your thoughtful comments.