inb4: "but ads fund free open web" - I can live with paying subscription for every single site I really want to visit (even huge subscriptions if the site is that good). There are very few of those. AND many "free open" sites do not have ads even now.
And by the way, please define "rich" and "rich enough".
The fact that results from these smaller sites show up in google searches (i.e not behind a paywall) is a good thing for the web in general as they often have good content, a few non obtrusive banners at the bottom seems like a small price to pay. If a site just bombards me with aggressive advertising I simply don't go back, these sites rarely have good content anyway.
I think that having access to free high quality information for people of modest means is a big net win for society at large, but maybe I'm just a socialist..
One individual has at most 16 hours a day for internet and if someone would estimate average times that the discrete number of sites to visit would be rather low. It is entirely possible (not 100% sure) that after initial shock communities will restructure a little, some really obscure sites with little unique content or services will die, but users won't leave. they'll just shift to occupy all the sites they really want to visit.
And right now I see that small and obscure websites are NOT findable in search engines. They don't do SEO and SMO, they are totally dominated by ad driven monsters they produce and produce and produce... well something. Sometimes good content sometimes not. Mostly not actually. I almost never find really good unknown stuff in Google&Co, only by direct links from friends and random people. Such sites are like dark matter of the internet, real but invisible knowledge. Invisible behind the noise from ad giants.
Remember the site expertsexchange.com? The Q&A site that put their answers behind a paywall, now remember how stackoverflow ate their lunch with a few small unobtrusive adverts.
I actually do find plenty of useful content on small websites, phpBBs & blogs through google. Sites with unique content tend to rank well especially if you are searching for specific terms.