I am really against of advertisments at steem. Because if we allow it, what would be the difference between steemit and facebook?
But if it will be allowed I think the advertisement shouldn't be centralized. It might be a choise of the content creator to allow ads in the post or not.
There could be a marketplace for ads where you can licit to advertisment space, and you can buy it for STEEM.
Also the money should go to the community like the rewards now.
Totally agree with your last point!