The more I dig into this the more mind boggling I find the decision to sunset G+
- What happens to all those buttons, badges, embedded posts and signins for G+ on other websites?
- How do you extract and archive content from within communities?
- We now need APIs to extract and archive non-public data.
And so on.
Pretty much everything here is going to sunset as well.
https://developers.google.com/+/web/
And in the short term, Takeout is incomplete for archiving and extraction all that G+ content. So it may require code and the API to get at some of it. Except that the API is incomplete as well.
Any automated migration facility to another platform is going to have to use the API. And there's not much time.