I think you're wrong on this. Facebook will definitely be around for a long time. It's already lasted longer than any other platform
nah I think facebook, twitter AND instagram have stabilized as far as new people signing up on them. They have their crowd - all 3 are not nearly as active as they once were but they have enough people on there to make it seem so.
I have 2000 facebook friends - most recent stories will be a slow news feed day on facebook outside people posting videos. If you notice facebook has switched to "top stories" when you log in. Which will display the posts from your friends with the most likes/comments. To make it seem like its more active. You have to manually switch it to "most recent posts" which is insane because thats what most people on facebook would prefer
I currently follow 2500 people on instagram. Before if I hit refresh there would always be a new picture. At worst 1-2 minutes would pass before a new picture popped up. Now I can go 20-30 minutes on my time line before a new picture pops up. 2500 people.. That means in 30 minutes, 2500 people did not care about instagram. Thats crazy drop off from just a year ago and in 2012-2013 people were practically spamming photos. Back then it was also used for more. People would post pictures of their food, sneakers, bridges, landscapes, etc. Now people either repost their snapchat videos/pictures or its just a selfie - Maybe a group picture for a happy birthday.
Twitter only poppin when a big social event going on. It spikes. The people with 100k tweets will always use it but I think the days of people signing up for twitter and pouring their minds out in tweets like before, are long gone.
Snapchat is the new wave right now. and in 2018 it'll be something different. Snapchat has stolen Instagram shine which to me is crazy because its less interactive as far as typing goes but its pretty much like a selected facetime

I dont personally like it much but I get the appeal , I guess.
Just 2 years ago most people would think nothing could be as popular as twitter, facebook or instagram. Snapchat came through and crushed all they buildings as its the current trend. But like I said by 2018 we'll be on to something different. The only thing thats changed is the speed we move from platform to platform. Its slower than what it used to be.
and yeah while 2000 facebook friends and following 2500 people on instagram isnt "everyone on those platforms" I do believe 2500 people ages 21-40 is big enough sample size to show that people are starting to not care about instagram and facebook anymore