My thoughts on the plot

I do think the MUTOs are ancient creatures, and ancient enemies of Godzilla. I think when the US navy tried to kill Godzilla in 1954, the MUTOs were mutated. Which means, the MUTOs aren't man-created, but man ENHANCED. Also, based on the Soundtrack, Godzilla will live, and maybe the shot of the teaser trailer is the near ending/ending of the movie. Or, Godzilla's last movie scene will be when he goes back to the sea. 

I do not think Godzilla caused the Janjira incident. He's too big to NOT be noticed, right? The MUTOs are way smaller than Godzilla. The MUTO seen in the WonderCon footage seems small enough for the humans to see it. Also, there are not 8 legged MUTOs and winged MUTOs. There is one 8 legged, winged MUTO and another bloated-centipede thing with a beak from the first TV spot "It can't be stopped".