In your honest opinion how long do you think Pokemon GO will last

[Shiken]

It depends on a few things really. How often will new pokemon be added? When will we get the patch for trading and battling other players outside of the gym? Will there be group battles? What events will be held in game and how often?

If all of these arive in a timely manner, GO will last too long for an acurate prediction being F2P. However if they fail to add features and hold events often enough, it will fade sooner rather than later. Only time can tell for now.