Yeah, I feel like they set themselves up for a tough situation in a few weeks. Ingress was in beta and invite-only state for ages, which allowed the map to be built up and people to slowly join over time. People who joined later were still excited about low-level peers starting with them.

P-GO is likely to reach its peak in a few days... If some exciting content updates don't follow they may have a problem keeping people around. They'll definitely retain many fans (people still play the original handheld versions), but it will be interesting to see what happens in the future. Also, from own experience - it was easy to play Ingress and go on long walks initially. But after a while, you really want to spend time doing other things; past some point a 1h trip to do something specific for virtual points loses the appeal.