Engines as Gems?

There’s been a lot of talk lately about releasing Rails plugins as
Gems, instead of putting them in vendor/plugins. I have to admit, for
a few reasons this seems attractive.

Has anyone given any thought to how this might work with Engines? I
have a few engines that are used by all my Rails applications. It
would be nice to deploy them as Gems. At the very least it would
speed up the deployment of my applications.

It would also allow me to push bug fixes for the engines without
having to redeploy all my applications. Symlinks could work for this,
but if I ever wanted to lock an application to a specific version,
things get messy.

It’s also a better release system, if I ever wanted to release my
Engines publicly.

Any thoughts?