I guess we will have to see what will happen. Perhaps one of the other front ends will monetize and run ads in their system, such as busy.org. They can auto add "Posted by Busy.org" to the tail of all the post from their site (as many other front ends do also), so it should not be hard for them to add advertisement banners to the top or bottom of a poster's post.
It does not all need to be on the top of steemit's front end. An ad placed in this manner would still be visible on all front ends. Look at the footers of some of the posters, some of them have a lot of "banner's" at the foot of their post advertising this or that service or page or program.
posted with partico
posted with esteem
posted with Busy
Posted with steeve
These are all micro ads.