It could end up like Bitcoin where they have had a lot of competition with new crypto currencies improving on what they have done and they still maintain the top slot.
Maybe Steemit can do the same as they have a head start, but then again they could fall away to the way side like MySpace did.
As long as Steemit can give the public what they want (like Facebook did) then it could go the way of Facebook.
Only time will tell as all we can do for now is guess and speculate.