You’re barking up the right tree, at least, but it’s possible the Arduino IDE has moved on since I last built the firmware and broken things. You might find that just deleting
#include <Keyboard.h> makes it build, but unfortunately you’ll also find that the pinout for the kickstarter board differs enough from the retail that this firmware wont quite work.
Actually I thought I’d dropped that line ages ago!
It shouldn’t be too tricky to get the retail Picade firmware working properly on the Kickstarter board. Just a few pin swaps and some extra buttons to add in. Could have sworn I made a start on this somewhere. I’ll try and look into it this weekend.