I'm really glad to hear my idea was helpful!
Playing FNF on mobile is essential for me to pass the time at work, and I've put a lot of thought into this because options like V-Slice can be cumbersome (requiring me to find specific mods).
My major is actually game development, but I'm a graphics major, so I know next to nothing about coding. When you mentioned 9k+, it just sparked an idea from a design/layout perspective. I thought, "To press that many keys on mobile, wouldn't it make sense to adapt the layout to the human body?" You know, similar to the concept of ergonomic keyboards and mice.
Of course, I'm not saying this is the perfect solution, and we'd have to playtest it to know for sure. While aligning the angles to the thumbs seems ergonomically correct, I do suspect it might cause significant thumb fatigue.
Still, I hope this idea can serve as a good "first draft" that sparks even more and better ideas.