Interesting concept. I feel like I'd be ok with it? I want to say we should bind `nil` to `'()`, so existing code would continue to work, but I might be overindexing on compatability and what I'm used to.
I will admit to not being super sure what the real differences between nil and '() are. Presumably it's more than "what is the human-readable representation of the value that terminates a list/is the false value". But I'm not sure what. Also, is there a difference between the quoted and unquoted version? It feels odd to write () in a repl unquoted -- usually, I expect parens to mean a function or macro call.