Only the relays, clients, and profile builders would have any need to be involved as they would own the digital real estate and there's no reason for all 3 to be a packaged into a centralized system. They can all be different #advertising channels at different levels of the network.
A boosted message is kind of like an #advertisement on a relay already.
There's plenty of space on the UI of clients for each (that wants) to come up with their own ad layouts, rates, rotations, qualifications, and targeting parameters. Clients will be/already are different companies and organizations anyway.
Profile builders can also come up with their own advertising setups as well.
I don't know why I would pay a user to view content/ ads. That is not a service and the fact that I am paying them obliterates the concept of intent. The point of paying for the ad is for the publisher to place it somewhere that is highly visible to an audience with intent/interest enough engage further. Hence, the payment being on the click.
The better the placement - the higher the relevance of the ad to the audience - the more clicks the ad gets and the more money the platform will get from the #advertiser who is paying for them. That's is how the PPC business model generally works. It does not pay to serve irrelevant ads.
Paying a user to view #ads is just paying a rando to view ads. It's devoid of intent - there is no targeting or point in it. It just becomes about a user siphoning money out of businesses, not engaging with the product, service, event, community, etc... being advertised. It's a pit.
Ads don't exist just to be seen. They exist to present something new and of interest to people who already care about that thing in some capacity. Its about building up community with people who like a thing and want that thing to continue to exist because it adds value to their living experience.