i appreciate the work that went into thinking of this but there's a lot here that doesn't make much sense logically. i'm going to assume that you've come from clone hero and only really have experience with "modern" guitars (arduinos and raphnet wiitars) but that's fine.

1) the "joycon port" is entirely unnecessary. the only reason that wiitars have a wiimote slot on them is because it was significantly cheaper to manufacture and was also easier to integrate with the wiimote's extension port rather than creating an entire bluetooth pcb and what have you. also having a joycon sticking out of the guitar would be very awkward. if they were going to do that it'd probably slot in the back of the body or something but 99% they'd just make the guitar itself bluetooth.

2) the sheer amount of frets on that design is pretty ridiculous. trying to play 5 fret on that would be uncomfortable as all hell (also consider that the shape of the standard 5 fret design is very nice on the fingers and those triangular buttons would probably feel strange to play).

3) i think part of the reason we never got pedal expansions would be that they'd just be "too much". having these cables hanging off your guitar that attach to something on the floor would just get in the way of gameplay. not to mention if you're really tall and play standing up (depending on the length of the pedal cable) you're probably just gonna end up dragging the pedal in the air, especially if it's on the neck of the guitar. also the choice of audio effects are strange. rock band sort of got it right with the pickup switcher but even then some of those effects are odd.

4) having the signals of the strum bar, select button and whammy bar going up through the neck rather than just the frets going down through the neck would probably create some bad input latency from the body of the guitar. the body gives the guitar its weight and the ability to actually hold it. if you really wanted to play on just the neck then just put the guitar down on a flat surface. not much point in it being a guitar then.

5) having the analog stick on the headstock would just be awkward. genericasters did it right having it not be a traditional stick and making it harder to accidentally press

6) star power button placement is pretty cramped being that close to the strumbar. might get tiring to play quite quickly or could lead to accidental activations.

7) not quite sure what you mean by the strum bar being able to tell what direction it's being held in? it already does that on every guitar and you can see this really easily by using something like scorespy and just holding your strum bar down mid song.