Nope, still doesn't work rcube::get_instance is still in there.
I'll admit, I have only dabbled with the plugin framework thus far, but I have been/and will be going through the docs to get up to speed on all of this.
I definitely think roundcube is here to stay and worth the effort to contribute more. I've been burned by other projects in the past, but it seems to me that roundcube is starting to become a killer app in the webmail space.