I'm inclined to see it more like a Metroid attraction for Nintendo Land 3D, than a Hunter 2 sneak peak.
Yes, I think this is closer to what this is.
Look at the beginning of the trailer, where the player character enters its mech. The characters head is obscured by a helmet or something, but that definitely isn't a Metroid character - I've been freeze framing a bit, and it looks much more like a Mii. The theming is very obviously Metroid, but not exactly fitting.
So I agree with Aostia - Nintendo Land 3D, with slightly altered interpretations of the games from the WiiU version (maybe even some different franchises compared to the original). Makes sense to make a spiritual successor to Metroid Hunters for the 3D version.
Given that this seems to be a FPS, it might be a New 3DS exclusive, given the dual control sticks.
Announcing it as a standalone title at the World Championships just seems like Nintendo teasing a bigger E3 reveal, playing on the competitiveness, the success of Splatoon and the slightly 80s vibe of both the game and that event.
Or it's just its own weird little thing. This is Nintendo after all.