I love the ideas in this keyboard! The operator layout is pretty awesome as it is, but I would personally put Home, End, PgUp and PgDn on Fn+Arrows. That layout is much easier to remember and I can say from experience that it's a blast to use.
Integrated slidebar is super cool, as well as the usb hub and USB-C! Not sure about audio amplifier, though, that seems a little out of place. I also like the lengeds you made for backspace and delete. Phase is also cool. Fn seems a little busy the way it is, but not a major turn-off.
How would you implement the Phase key in software? I know some IDEs support stuff like this, but it seems to work slightly different with all of them.
F0 isn't an actual key as far as I konw, but it goes up to F24, that may cause some confusion. Maybe make F0 send the F16 keycode? Would make sense in terms of a 4bit unsigned integer overflowing from 16 to 0.
Unfortunately, this will probably be way too costly for myself, so I'll be following this, but won't buy in. Good luck!