That sounds really cool! I'd love to see it when you've got something more concrete. I assume you're already aware of the KeyMouse and the AlphaGrip?

https://www.keymouse.com/ https://alphagrip.com/

I don't think the layering needs to be as big a deal as one might assume. I mentioned in the post, but in many ways I think layering is easier to deal with than larger keyboards, and not only that but also culturally small-keyboard users are increasingly okay with using layers, e.g. the tiny-keyboard gamer crowd, or even most laptops now have a dedicated Fn layer in addition to the traditional shift, ctrl, and alt. So long as you don't go overboard with it I think it shouldn't be that intimidating.