I can't speak for everyone, but I think most of us are pretty sure it's Jangmo-o. It looks like it has a gimmick that's going to be more emphasized in its evolutions (the heart).
What really gave it away for me was the official description: "In its pursuit to become stronger, it never neglects its training". That whole training to become stronger thing just screams big bad___ final evolution. If I'm not mistaken, Bagon had a similar description. Maybe it was about wanting to fly or something.
I'm a little disappointed because I was hoping we'd get another type-break. Metagross was such an amazing creation. Here's fingers crossed we'll get two!