Hello,
I went through the pdf attachment describing the flow of how you manually extract the emails (public) from list of followers.
I think this can be automated via a chrome extension.
Implementation proposal:
1. I'll build a chrome extension which loads on [login to view URL]* domain.
2. The extension will load on the Google+ community page and in the toolbar, clicking on an "Extract Emails" button will start the work of web scraping and extraction of email IDs of followers in this.
3. Might need some sort of iframe creation in the DOM of the page, to be able to load the profile pages of users because the Email IDs are only available on clicking the "About" action on their profile pages.
As of now my initial analysis says that this sort of scraping should be implementable. If we do go onto work on this together, then i can do more in depth analysis and figure out any show-stoppers.
Hope to hear back from you.
Cheers!