The question is not about something being guaranted or not.
The question is:
Steemit is a new social and a new currency, is it going to be interesting for the average person ?
If the answer is Yes, than Steemit will be a great success.
If the answer is No, than Steemit is just going to be a big flop.
The answer could also be neither, it interests a fairly large niche, but a niche nonetheless that has influence. A lot of people will find this site useful and interesting. But most just want to post baby pics (or other major life events), get angry with politics or try to get laid. And most people like facebook's upvoting system where you like almost everything and you don't ponder over your upvotes, it's more social there way.
The chances are better that Steemit ends up being something different than what the designers imagined. They started the rock rolling, and try to direct it, but ultimately it's not in their hands anymore.