Beyond the ip based ad block killing implications, this would also allow google to collect more data about chrome user web traffic, while even more significantly it allows them to obsfucate this data from their competition.

Have fun analyzing user data when google gets the real feed of it and you get whatever they choose to let you see. There's nothing preventing them from messing with more than just the outgoing IP.

Google gets to pretend they care about user privacy when they're really just trying to hinder the competition.

The rest here is pure speculation on my part, but I don't feel google deserves the benefit of the doubt.

There's also potential here for google to use their spot in the middle of the connection to effect what you see when you browse the net. Could be pure censorship, inserting more ads for themselves, or something more subtle.

They could quietly direct more traffic to sites they want you to see and away from what they don't, even more than their search already does.

Marketing and internet usage studies show that even a minor delay of a few seconds when loading a page can have a large effect over time on whether a user will return to your site. Introduce nearly invisible throttling on some sites and boom, you can move the needle on competition between sites and ecommerce.

There's some chatter on net neutrality being enforced at the ISP level, but does that apply to VPNs?