I wrote in another article that Steemit might become a platform that allows advertisers to purchase advertising from content producers with steem currency, and that if this does happen, it will serve to back the currency with tangible value.
The key to this working is ensuring the platform is setup to require appropriate payment in the same currency that is awarded to content creators. I don't know if this is even possible but I hope that it is.
This idea can work with other platforms too. Again, the key to this working is that any time value is produced, the platform must be designed so that the only way to get that value is to purchase it with the same currency awarded to the producer of that value.