You underestimate how stultifying size can be. When I was at Google, pretty much everyone cared about how the internal incentives were screwed up. There were a lot of attempts at changing structure of promotion and career development, but nobody knows how to do it. To be fair, I'm not aware of any entities of that size who don't have the same problem of with balancing the need for centralization with keeping bright workers motivated and growing.
Why not just place a product manager above each product (Gmail, YouTube, Play Music, etc. etc.) that each report to the master manager who's only job is basically to unify all the services and make them work together in a nice way. He would be the one to force everyone to use the same animations, same icons, same conventions etc.. honestly I never understand how companies with millions of dollars can't come up with the simple fix of 'give an experienced person total authority'.
