I remember back in the 90s N64 magazines were always posting rumors about the “Dolphin” console that Nintendo was supposed to be developing, which eventually became the Gamecube. Nintendo also was more open back then, with their famous Mario 128 tech demo for example. Also the Nintendo DD rumors were huge as well, which turned out to be a big failure and never released outside of Japan.
There are a lot of decades old embedded systems out there. Every so often you hear about a big company still relying on floppy disks and other old tech, including major railways and airplane companies. Having the source code will help with debugging better than having to disassemble or other reverse engineering.