I asked @Shelenn Ayres about this topic recently and your name was suggested.
I'm in a conversation with a g+ contributor I really admired to see how his migration effort was going. He's a prolific photojournalist (and IMHO a brilliant one). He seems to be struggling with getting his content from Google to somewhere else.
Is there a system with a conversion tool to go from HTML or JSON exported posts and linked attachments (photos, etc.), directly into Friendica, Diaspora, Mastodon, etc.?