I imagine if this was a Star Wars Rebellion v Empire game it would be pretty equally as big.
I doubt a Star Wars game in a similar vein to this or Ingress reach something like this. What would players be acquiring? Droids? Rebels and stormtroopers? Jedi and Sith?
The charm drawing in a lot of casuals is finding Pokémon and trying to catch them. It's not as interesting with other franchises. Case in point: Invizimals, though that probably also died because it was on Vita.
Most people haven't even tried gym battles because there's no attempt to explain how they work in-game.
There'll be copycats, but Pokémon is unique in that it's already a huge franchise beforehand and it's got a large range of likeable creatures, some of which most people are already aware of even if they never played the game.
there's three factions; ingress only had two, right? I think most stuff is red/blue right now but I expect the balance might flip around a bit, hard to tell without live servers here
Team numbers seem to be the same everywhere: Blue => Red >>>>>>>> Yellow. I'm told this was even true during the field trial beta period.
On the FB page for the PokéGo Walk, there was a poll on teams and red and blue are fairly even in numbers while yellow has less than half of as much members.