Sounds like a fun project!
If your thoughts was to make a portable Raspberry Pi laptop I don’t think you can achieve that as the parts you’ll need will take up more space than the system offers internally!
So what will it require??
First the keyboard is just the raw switches which the logic on the trackpad converts to a USB2 signal with the trackpads signals which feed into the logic board. So you’ll need to take these USB signals to your Raspberry Pi logic board and create the needed keyboard & trackpad drivers so the Raspberry Pi understands the signals, lastly the needed power for the trackpad USB conversion logic.
The display ribbon cable which connects to to the logic board carries the LVDS signals generated by the logic board to tell the LCD T-CON board how to paint the image onto the LCD. It also carries power for the T-CON logic as well as the most important power for the LCD backlight at the required intensity level (dimmable).
This doesn’t get into the power services the converted laptop will need (AC or battery)
Thats a lot of pieces which you need to emulate in replacing the main logic board.
Find the schematics and boardview drawings for your system and study them see if you can figure it out.
You can find LVDS conversion kits to reuse your laptops display. Using a standard keyboard and trackpad will also work so while it all won’t fit into the MacBook Air shell you could get your Raspberry Pi working!