IPython and other reprs are an entire abstraction layer on top of Python, which allows them to do a lot of extra things like implement new commands and alters a lot of behaviours, but the CPython REPL is just the interpreter evaluating commands, and this is very coupled with the regular machinery, at to the point that is the tokenizer the one consuming input (lazily!) from standard input.

Unless I am missing anything, the only way to do the desired behaviour is to re-architect part of how interactive mode works or to directly make exit a keyword, which is backwards incompatible. 

I may be missing simpler ways of course, but in general, my opinion is that anything that involves modifying the compiler pipeline to somehow special case this is too much cost for the advantage.