> when using unload-feature), so yes, ideally Emacs would make it
> possible to have multiple versions of the same package.
Having multiple versions *installed* has been supported since "for ever"
(AFAIK support for that was added very early in `package.el`s life,
before Emacs-24.1).
Having multiple versions loaded at the same time in an Emacs session?
I think we're very far from supporting that.
BTW, rather than unloading, `package.el` relies on forcibly "re"loading
from the new version the already loaded files from the old version.
It suffers from a different set of problem :-(
[ I suspect `defvar` is the main problem for that solution. ]
Stefan
