hmmm so Google will stop being a de facto monopoly while ad networks crumble? Maybe free and/or open search will start flourishing again because finally there is incentive to write readable HTML for all crawlers instead of only returning scannable results when they detect the (highly peculiar) GoogleBot.
Maybe we'll get search engines again that do proper ranking (I hear actual pagerank was not a bad idea), or ones that do a proper AND-search of your keywords instead of trying second-guess you. Maybe they'll even return more than the top 1000 results. Search engines aren't that hard if you don't try to be as big as Google immediately and they just try to be good at that things they're good for.
Walled silos of user-supplied data will fall apart because it's no longer a viable strategy to special-case GoogleBot access to get your locked data appear in the results any way.
Google can no longer afford to arbitrarily overlook tactics which are against their TOS, as long as the player is big enough.
All the while, small business can still advertise if they want, easily enough by making a deal with other businesses (perhaps through a middle-man) and self-hosting the banner, click-through link to the other. Maybe some self-hosted analytics. And because in this hypothetical dream-world the craziness of these huge 3rd party ad-networks is gone, this will actually work, it'll pay, people will click.
Ads will therefore become much less shady as they are currently perceived (like, merely deceitful, not as a proper possible danger to your computer, your data and identity). Hopefully this will change the public idea of what ads can and should be in such a way that these ridiculous 3rd party ad networks with their "accidental" malicious code and ubiquitous tracking will never get a foothold again.
There might also be some downsides, though.