1. Great that you're trying to implement this!

2. But I really recommend that you try to structure this as a 3rd party module first rather than patching the Python distribution -- it's much harder to get accepted.  Or as a pure-Python patch to asyncio, rather than patching the interpreter's C code.

3. Which Python version did you use as a starting point?  The patch doesn't apply cleanly to the repo head for either Python 3.4 or 3.5.  If you used a source distribution, please switch to the Mercurial repo.  I recommend 3.5, as this is a new feature.

4. If you really want to patch Python, you need to add docs.  In fact, I recommend writing the docs first.

5. What on earth is going on in your input() coroutine?  You create a Future and then immediately yield from it.  How is it becoming done?

6. Surely all that C code you are adding to readline.c was copied from some other place.  From where?  Perhaps it can be refactored rather than copied?

7. See #2.