This instance should definitely exist, but I think it would be better to print the contained Int in hex format. Do you know if that's possible now, or will we need to add a dependency?

https://pursuit.purescript.org/packages/purescript-integers/3.2.0/docs/Data.Int#v:toStringAs would do the trick. I think, there is an advantage of displaying the Unicode representation. Maybe a combined version?
(CodePoint 0x... - "∆"). That way you can see if you have chosen the correct number for the symbol you wanted.

I think it would be best to just use the Int, to keep it simple, and to avoid suggesting that there's anything more to a CodePoint than just an Int. People can use singleton if they want to see the code point as a string.