nadvice.el: making add-function applicable to key-binding / using a function as generalized value

[Pontus Michael]

First problem that I would like to address with this proposal, is the
inconvenience faced by the user attempting to alter default args for
existing command.

And secondly, wouldn't it be logical to expect following form to work?

    (add-function :filter-args
          (key-binding [?\M-\(])
          (lambda (args) '(1)))

If my understanding of how this kitchen works, it would only require
implementing gv api for `key-binding' for this to work and probably
`lookup-key' along with it.

My knowledge about involved technologies is very superficial, and my
hope is that someone capable will also see the benefit in it.