Yes, that's how I see it playing out too. There is so much user input, and such an incentive to build onto Steem, especially now that we have @utopian-io, that I can't see how these kinds of marketplaces couldn't happen.
Once real social media players, like the big YouTubers and Insta stars come onto here, there's going to be an insane demand to find a gateway for them to spend their Steem earnings for real world goods and services.
If Steem lives up to it's potential to be the next Facebook, it could literally become a global currency that people transact with, and accept payments in just like a regular bank account.
Steemit will have to add a lot more features to be a threat to facebook in my opinion. At present is a like a reddit on steroids. Personally, I think that Zappl and Dtube have greater potential for shifting people over since they are simple interfaces hence very little learning curve. Give them a bit more time to work out the bugs and they will be ready to crush it.