>>>> Why is this a patch that uses advice and hook instead of a user 
>>>> option that changes the behaviour of icomplete directly?
>>>
>>> Because it's the simplest / cleanest way to do it.  It's a kind of 
>>> derived minor mode.
>>
>> Advice is not entirely unproblematic though, so the recommendation is 
>> usually to avoid them in libraries for use by others.  Even more so in 
>> Emacs itself, I think.
>>
>> See the ELisp Manual sections `(elisp) Advising Named Functions' and 
>> `(elisp) Coding Conventions'.
>
> Indeed, we prefer not to use advice in our own code.
>

Okay, I did not know that there is a strict rule against advice.  Here is 
the updated patch, which uses a hook instead.  This makes the code even 
more flexible.