Google doesn't know when you will update content on your site so it has to almost constantly hit it with crawler bots. The idea would be to move towards a push-based model wherein sites could push updates to an open index instead of waiting for bots to crawl the site and use up extra bandwidth.

Of course, if this is the primary issue, I don't see why Google couldn't just implement a closed push-based index. When your site updates, you push the changes to Google. The index is still closed but it solves the bandwidth problem without opening Google resources.