Hiding in the ox-taskjuggler thread is a discussion of some of the problems
caused by having contrib bundled up in the org-plus-contrib package.  (See
that thread for the details.)

However, a general question remains, as asked by Tim Cross, whom I will
quote if I may:

There are also some other alternatives on the emacs-devel list from when
> I asked as a general question regarding package.el and dependencies.
> Should be noted that this issue is primarily caused because, fro the
> package.el perspective, org-plus-contrib is different to the org
> package. Other ELPA/MELPA/etc packages have org as a dependency and not
> org-plus-contrib. There is no support in package.el for alternative
> dependencies.
> I would be interested in understanding the rationale for having
> org-plus-contrib rather than just an org package and an org-contrib
> package? It should be possible to just have an org-contrib package which
> depends on an org package (of same version). This would then avoid this
> issue. As this is an obvious solution, I suspect there is something
> subtle which unpins the rationale to have an org and org-plus-contrib
> package approach, but don't know what that is.


So, is there an answer to this good and as-yet unanswered question about
unbundling contrib into its own package?

cheers,
Simon