We all kind of discussed this topic before but I don't mind talking more about this topic.
I honestly wouldn't mind Godzilla and Kong fighting all through the film. They did it in the original, that seem to work out great! But we all know no one wants to see either Godzilla nor Kong lose. So yes I do think after a long fight between them another threat will show up and bring them together.
OR...... maybe their common enemy is... man! Maybe the Oxygen Destroyer is unleashed on both monsters as they fight towards the end. Maybe it will be a close finish between both monsters and before the final blow to each monster is struck, Monarch unleashes the OD. Pinning both monsters into submission. We might not see a 3rd monster, or... a clear victor.
think about it, in a lot of "VS" films, the common threat to both parties always wins in the franchise's that made them so popular to begin with. For example:
Freddy Vs Jason - Teenagers Won(they always win in the end don't they?)
Alien Vs. Predator 1 and 2 - Humans Win (they always do).
Frankenstein Meets The Wolfman - NO CLEAR VICTOR
I'm going to ignore the Full Moon entries on this one. Most of the "VS" are very silly. Puppet Master vs. Demonic Toys, Doll Man vs. Demonic Toys(spoiler alert, Demonic Toys always lose). Gingerdead Man vs. Evil Bong(I did not see but Im sure its silly and the humans win).
The only movie with a clear victor at the end of such a "VS" movie is... King Kong Vs. Godzilla(1962). Where we see King Kong come out of the sea swimming back home. Clearly Kong won(just barley). Hence such a dramatic need for a rematch between the two. Keep it the same. 2 monsters enter, one or none leaves.
But I think the only reason we are really discussing this is because of Batman Vs Superman. They team up after a pathetic 10 min fight scene. Leaving no victor and no loser. Everyone happy and no one is upset. Lame.
But what ever happens in this VS movie, we should just enjoy the ride. This ride only comes around once in close to 60 years, so lets just enjoy it while its here.
But as much as I would love to see a team up between these two Monster icons, I hope they do not succumb to that. the title is called Godzilla vs Kong, not Godzilla and Kong - Fight for Earth, I hope they keep it one of a kind.