Interesting idea and I think it could work. Especially for bloggers/vloggers who have something to "sell" and want to pay to have their product or service displayed prominently.
This could be built as a simple "bolt-on" for existing ui's like beblurt and blurtblog, so it is more decentralised. Then, all ui's in the future can use the bolt-on too, on their own sites and even charge some sort or tiered-pricing for prominence.
There would be no need to build anything since this is already part of Nexus. We just have to add the API calls on the frontends, and possibly modify the code in Nexus if it doesn't already work the way we want it to work.
See my reply to @khrom above for links to the relevant code in the Nexus code base.
I think it could even work better for people from outside. When someone tries to advertise something, they often look for different groups of recipients in different places. We already have quite a large group. If outside capital tried to advertise here on blurt, it would lead to an increase in demand for blurt on the stock exchanges.