What a crazy number of servers they (might!) have! If those numbers are correct or at least good ballpark figures it would be interesting to see utilization stats.
I heard that generating video stories (the slide shows of your year for example) came from a hackathon project to keep utilization high.
Anything that can be done as an offline batch process is great for utilization. That’s how most of the cool things in Google Photos are done too: automatic visual effects, movies, location inference, facial recognition, etc.