This is an interesting topic. And I agree, the title should be about BBS in general, not just phpBB, but that's not of utmost importance.
Although social media as a term usually refers to Facebook and the like and not BBS, I agree that BBS are social media, too. The term just wasn't around 15 years ago (AFAIK). That's not important, either, just as long as everyone understands the terms the same way.
I also agree that BBS and other social media can coexist. Although they serve some of the same functions, they also have their differences. In BBS, users are posters among other posters, whereas in newer social media users have their own personal page. That's one huge difference and one that tips the scales toward the newer social media. It feels good to be the king of your own page, and there's nothing wrong with that. We are human beings.
Information overflow and especially "information" overflow is staggering nowadays. That's a problem unless one knows how to handle it. That definitely works in the favor of BBS.
Another difference related to the above is the visibility of information (or "information"). That's where BBS take the cake. You can read posts from years back with ease using BBS. With newer social media, it's all just about gone usually in a matter of hours or days.
And there's a problem. One of the founders of our site recently logged back in after a long hiatus. He has been around the Internet since the days of newsgroups, and he is a man of words. Even he said that this newer social media has shortened his attention span so much that he cannot participate in BBS anymore. He wasn't happy about that.
The future and phpBB? I would think that tagging users and liking posts and topics should be a part of the core of phpBB. Those functions are very popular in, say, Facebook. They were very popular on our phpBB 3.0., and our users miss them.
Another welcome change would be incorporating some sort of phone notification method. There was an EXT in the works for this, but unfortunately (and understandably) it was abandoned recently.
We have WordPress, phpBB, a Facebook page, a Facebook group, and a WhatsApp group. They do not work flawlessly together, far from it, and they serve different functions, but I think some sort of bundle like that works the best in today's virtual world. phpBB has always been and still is the heart of our site and community.