From the trailer we don't KNOW it's the Enterprise in the water - all we see is "NCC" - and we do see a Federation starship shape crashing into water, apparently on Earth. But the engine struts look like they curve downward - I doubt it's Enterprise.
Yeah, the ship crashing into the water is not the Enterprise. That much is certain. The nacelles are too square-ish and are lacking the big fin-like intercoolers on the back. Plus, as you said, the pylons are wrong.
Judging from the trailer shown during the SuperBowl (I didn't watch the game, just the ads and the halftime show ... and the lights going out), the ship crashing into the water could VERY WELL be the Enterprise. The Enterprise -- registry NCC-1701 -- has suffered some serious damage, and is plummeting into the atmosphere. Conceivably, it crashes into the water, sinks, they make repairs underwater, then it rises back out of the water.
What do we know about the foe? He's a humanoid male, and is self-described in his exchange with Kirk as "better at everything". Which old foes would fit that description?
Gary Mitchell (as several have speculated)
Khan (as several have also speculated)
Norman (head android from "I, Mudd" -- that would put an interesting spin on the new movie)
Roger Korby (his android duplicate, anyway)
I don't think Garth of Izar would fall into that category -- he was simply a brilliant starship captain, but not better at everything (including physical - it is also known that he can withstand a Vulcan nerve pinch)
He also says, "You think your world is safe. It is not." Now who of the above might say that?
I don't think Charlie Evans would say that. That sounds like a mature quote, and Charlie was pretty immature. But in the alternate timeline, perhaps Charlie was born earlier and has had time to mature -- and time for his feelings to sour.
And I don't think Roger Korby's android would threaten the Earth like that. Although this is in the altered timeline, the Old Ones and their equipment would be the same. Even Ruk could not remember that far back. And the equipment duplicated unaltered the mind of the original subject.
Now, if the threat to the Federation comes from within, that eliminates Khan, leaving Mitchell and Norman. Norman managed to infiltrate the Enterprise, passing as a new crewman for some time until it was the right time to take over the ship. But I still like the idea of seeing Mitchell again. They would have to make a trip to the galactic barrier so he could get the shock of his life -- him and Elizabeth Dehner, who could be the blonde.
I tell you what, though -- I think a good story might be to revisit the Federation/Klingon war from "Errand of Mercy", but this time they don't encounter the Organians. Can you imagine an unrestrained Kor bringing a Klingon invasion fleet to the core of the Federation? It would be glorious!