Hi @smooth, I didn't say ad-sharing is a blockchain feature. But it's so important to emphasize even in this post.
Actually it's so important to be considered as a part of blockchain feature. not ad itself but supporting ads, as many functions for steemit (post, voting, etc) is already part of steem blockchain.
Hope this clarifies my intention. (I also left a few comments on the current efforts, so my comment isn't irrelevant at all.)
ps. I contributed several across steem projects including the chain mentioned here, so I definitely know vendeberg is the head of blockchain dev (also know that you're an important person here). I also worked for ads team as an economist at Facebook. That's why I know and believe ad is very very very important. e.g., the main ad shouldn't be sold that way (by individual contract). ad-auction is needed. Of course, with the current resource of Steemit Inc, building own ad-auction is almost impossible. I understand that the current status is testing this and that. But eventually ad should be sold by auctions. (just using google's might be better than now eventually) Otherwise, it's very difficult to determine what's a good price to begin with. I believe that's one reason why the main ad's still almost vacant (I only saw some casino ad so far in the main ads).
Of course, I'm not saying that I'm right. Who knows? But I'm trying to help as a huge fan of Steem and Steemit.