You are welcome to add these things; we'll give you a generous extra 100 bytes.
Wonder if any student somewhere isn't trying to take up the challenge of adding castling to the code, using an emulator. I like to think that's something i would try to do as a student, because i'm pretty sure there's a tremendous amount of skill to gain by doing it.
True, but even "Chess lite" in 672 bytes is mind-blowing.