User blog comment:ChaosWarrior17/Destroy All Monsters 2.0!/@comment-24974663-20140523054826

I think it is very unlikely that we will see any extraterrestrial monsters any time soon. As it was already mentioned in the original 2014 film, we are most likely going to get monsters that are native to Earth and in a dormant state like Godzilla and the M.U.T.O. were.

That leaves the "Earth Defender" Kaiju, like Anguirus, Rodan, Baragon, Varan, Mothra, etc. Or entirely new monsters all together.

They could also use the classic plot point of using the corpses of dead Kaiju for weapons or experimentation. What could the US use the dead M.U.T.O. for?

If they do use Alien monsters, that needs to be a specific part of the plot, they can't use Gigan or King Ghidorah all willy-nilly. That's against Gareth Edwards intent of keeping the story pure to the original source material. But, in the spirit of keeping the series more "realistic" they may avoid having any kind of Alien or Mecha influence in the reboot at all.

Just my ten cents.