Gotham Gaslight

The suit, with its goggles and coat and emblem do not resemble the one from the Red Son. Instead, this new Batman v Superman suit resemble the one from Gotham Gaslight. And that is about all that can be said.

This might as well be a dream sequence (and we know that Zack Snyder is into them, and thus an alternate reality), in which Bruce Wayne imagines what would happen if Superman tried to seize power. And this dream shows him that he doesn't stand a chance against the followers, let alone against the Man of Steel (as you saw in the trailer, Batman is all but shown subdued by the soldiers).

So waking up from that dream he gives his speech to Alfred, about the preemptive strike, and dons his new mech suit, basically intending to become a piñata for Superman, waiting for Wonder Woman to come to the rescue.

This is a very thin theory for Batman v Superman, but it could work.

Check out on the last page the third theory!