I believe I commented on this somewhere here:
Take all the operations of the Steem blockchain: account creation; transfers, etc. Suppose a fee were added to the operation -- that would create revenue. Creating revenue at the application layer (ie. advertisements) for the blockchain layer is a more challenging matter.
what if... add fee to each transfer of STEEM, but leave SBD transfers without fees?
What about a smart contract splitting revenue. Something similar to what busy wants to implement using steem connect?
Like an eBay for Steemit where the app developer takes a % and another amount is sent to the null account?
Entirely possible with the blockchain, no?