Hi Bastien, 
I didn't follow this thread in detail.  But shouldn't it be enough to symlink e.g.  org-icalendar against ox-icalendar. As far as I understood emacs would prioritize those local symlinks over the system wide installation.  This would be a temporary solution until a new emacs release.  
Actually,  under Linux, this is a pretty common way to bend dependencies towards the newest version of a lib. 
Not sure for windows users.  

Instead of a simple symlink, the current dev head could have wrappers for those "old" files which bend the calls to the new files and issue a warning.  
That would help to identify 3 party code which needs some rework. 

Torsten 

Bastien <bzg@altern.org> wrote:

>Hi David,
>
>David Engster <deng@randomsample.de> writes:
>
>> Did you actually try that? How should Emacs possibly know that the
>file
>> ox-icalendar provides the feature org-icalendar? This will only work
>if
>> ox-icalendar is already loaded.
>
>Of course, you're right.  I reverted the commit.
>
>So the problems stay.  For third-party libraries developers,
>we cannot do anything else now than to ask them to update their
>code.  For the problem of Emacs autoloaded functions, org.el
>provides (load "org-loaddefs.el t t t) which should load
>the correct autoloads from the correct files...  but that's
>unstable.
>
>It seems the ox- prefix is a bad idea, you're right.
>I'll think about it again.
>
>Thanks,
>
>-- 
> Bastien