Keep in mind that steemit and crypto in general is still very early in it's development. Steemit ill continue to evolve and you just never know what it can turn in to. It literally could become bigger than facebook youtube and twitter combined one day, you just never know.
when the masses realize that there content has a monetary value and they learn about steemit they will come. The userface will continue to advance and will eventually offer more functionality than even facebook. Facebook is going down while steemit is expanding.
I don't know if other social media sites are necessarily on the down slide, so much as blockchain is genuinely revolutionary, just like Myspace and Friendster we're back in the day. Don't get me wrong, I hate Facebook, but they are building a strong foundation that will be hard to undermine. It might take another 50 years to fail just because it's big, like it did for Sears.
Steemit is great because of the blockchain, not just because of the money it provides. That being said, I'm sure we'll see a resurgence of value over the next year or so, just like we always do with interesting blockchain companies.
Whether it reaches the sizes of youtube or fb I am sceptical, however as you said it is still so early in the game. I am confident it will surpass the likes of medium however.