>> As I said, it's meant to be a derived minor mode, much like 
>> lisp-data-mode is derived from prog-mode.
>
> FWIW, we don't have a notion of "derived minor-mode" yet.
>

Yes, which is why I tried to "emulate" it.  I think it makes sense.  But 
it's not the point under discussion.

>> Using a user option would do the same thing as the minor mode, except 
>> that the changes would be scattered through the existing code.
>
> I don't see how.  I'd imagine a code like:
>

Thank you, that makes perfect sense indeed.

Thanks a lot also for your other comments, which I included in the 
attached revised patch.  The only thing I wasn't sure is whether it was 
intentional that you removed the :group 'icomplete from the minor mode 
tags, I think it wasn't, so it's still there.