I think I hacked marketing
I've built a system where websites grow each other. Your site promotes one. Another promotes yours. Think of it like retweeting or reposting websites. A network of sites sending each other free traffic and customers. Just a small minimal ad banner that sits on top of the website so as to not block any details of the website which the user can dismiss easily. The bigger this network, the more eyes on our products and the more customers. Whatever your product is, join the SiteAd network. You just set it up and forget about it, come back when you want to add another site.
The network effect is the interesting part here. If every new participant makes the distribution channel stronger for everyone else, that's a much more defensible idea than just another ad platform. The biggest challenge will probably be keeping the traffic relevant rather than simply increasing its volume.