Side note -- I went to a great talk by the Grey Area (Shadow Cities) guys at GDC, and one of their big takeaways was that you need to enable competition between people who aren't geographically near one another. Otherwise you don't build a critical mass of players.

I can't tell from the available material if Ingress gameplay provides for satisfying solo play, but if it doesn't they're going to hit the same issues Grey Area did originally.