Pull or push, a good search engine still needs a local copy of the web, and this is expensive. With a spider, search engines control in detail how they get cont

Pull or push, a good search engine still needs a local copy of the web, and this is expensive. With a spider, search engines control in detail how they get content. With push-via-notification, websites get much of this power. Is this something that Google wants to give up? Finally, if you're going to turn off your spider, /everyone/ better be pushing to you. So this seems more likely to be next-next-next generation.