How might Google monetize Ingress?

The first question I had when I heard about the Ingress beta was: why is Google doing this?

Face it: there's a real dollar cost to anything Google does, so it has to do one of the following:

1. Generate more revenue than it costs
2. Enable other Google products and services to make more revenue than it costs
3. Improve Google's positioning relative to its competitors, in order to generally benefit their other products more than it costs
4. Meet one of Google's non-monetary goals in a way that they feel is "worth" the cost and is offset by other income