That future is already here. I asked my 13 year old sister and her friend if they were on Facebook, and they both laughed and did an old person imitation of me! I couldn't believe it.
this "kids dont think facebook is cool" narrative has been going on for years, and it just doesnt matter. they come around eventually. the network effect is too strong.
Recently however, everyone's drifted away from it like they drifted away from MSN. The few kids that are still there just use it to tag each other in memes. Instagram is the new Facebook.
Source: Me - personal experience.
If so, what platform do they use for that?
Personally I get on Facebook twice per year, once on my birthday and once before summer to tell the world where I'm working.
That's about how it goes, then every once in awhile a new app will come up like house party recently, and everyone will jump on for a month or so then go back.
I don't see any point in switching to SMS now, especially when so many of my friends live in different countries.