People are already making applications for Steemit like Dtube and Mangosteem. I am not sure these will be the next big successors but they are being one of the first in their kind. Once EOS comes around it will probably make such platforms as standalones seperated from Steem, unless of course Steem as a currency would be linked. But either way Steemit itself will most likely thrive alongside those other services as a blogging website and things like crypto news. So yeah, it will continue to grow! ^.^