The Thieves and the 1000 Pokemon is heading towards Japanese 3DS units everywhere in the near future, and some more details have come to light as to how it actually plays. Or plays for you, as it were.
Firstly you'll grab a leader (Fennekin, Froakie or Chespin), and then you'll need to StreetPass immediately to get more Pokemon. StreetPassing constantly is imperative, as your supply will dwindle if you keep battling without linking up. For those of you who don't have many friends to Pass with, you can use Game Coins.
Characters from the upcoming Diancie movie will appear, and elemental strengths/weaknesses will still be a thing. So yeah, this is a simple free StreetPass heavy game. Still no word on an international release.