I no longer particularly like my patch, although something needs to be done. The easiest way forward is likely a (private) helper function in the readline module that can translate simple readline configuration strings to something that libedit understands and use that in the stdlib where readline bindings are replaced (but of course not for reading ~/.inputrc).

Comparing the libedit <http://linux.die.net/man/5/editrc> and readline <http://cnswww.cns.cwru.edu/php/chet/readline/readline.html#SEC9> configuration languages makes is clear that it is not possible to fully translate a readline configuration in a libedit one, but basic conifguration like setting up key-bindings should be easy enough.