It's fan art. There's always a chance they might turn up as secret characters or DLC, but they're not known to be in the game at the moment.
As for the reveal of both forms of Battra and Godzilla 1964, if I could post the clip from Predator of Arnold saying "
Dis is gedding beddah by da minute!" I would, because it really is!
I hope the latter will actually be available for us in the west though, either as a yet-to-be-announced pre-order bonus or just as an unlockable in the main game (especially since the European version only seems to be getting the 'instant access to LegendaryGoji' bonus and not the 'Showa filter' one that's also available in the US, though that also seems to be something you can just unlock through gameplay). I'd gladly pay extra to download it day-one if they just put it up on the marketplace, but hopefully this is just another early unlock thing and he's in the game for everyone regardless. Either way, great news!
Also, the official Japanese website appears to confirm that 3-player online multiplayer is also possible, not just 2, which means those sweet-looking triple monster battles won't just be limited to single player mode! Woohoo!