IPB is great, forums are great. I would never, in a million years, change forums for Facebook as an user.
I have a IPB board since 2007 with 220.000+ users that one day was VERY active, but now, every year that passes I have less activity and less registrations.
From what I see in my niche, people are going to Facebook groups, because everybody is already there. It's easy and convenient even for the most inexperienced user.
I think that the way search engines see forums is not helping our cause either. After panda algorithm, a lot of content in forums are considered "thin content" and content is king for better positions on search engines, but you can't control what 220.000 users wrote in the past 8 years (or will write). You can't block people that can't write useful topics and all topics can't be carefully manipulated by the owner in a busy forum. The majority of content in most busy forums can easily be considered as "low quality" by Google and this affect the whole domain, even the good content. (read google's guidelines)
Seo matters if we like it or not Less visibility in search engines = less traffic = less people knowing your forum exist.
I think that if forum companies don't come up of something new, we all know what will happen with forums in the next years