Come on in and lets talk about about all this.

Should we speculate of would happen if the Veil is broken by some unnatural force, like Discord's 'experiments'?

738221
Sorry for taking so long. Yes we can

I would think some organisations (mostly scientists and archaeologists) would want to explore the "New, exotic landmass" if the Veil breaks and Atlas is revealed to the whole world. And some politicians would try some diplomacy to meet the new nations/empires. And you could guess the chaos the news services would make.

Also, your headcanon is too good to not write another story with it.

781832
Ah... I forgot about the political ramification of Atlas popping up in the North Atlantic. There would also be some nations that would look upon Atlas with greedy eyes, luckily they are either on the other side of the planet and/or has no real blue-water navy. Also with the Concordiat's stance on freedom and harmony, and knowing the need for not just economical but also military alliances it stands to reason that the Equestriani Concordiat may join NATO.

Archeologically it would make a great impact with human made ruins that predate the written word and rise of civilization in the Fertile Crescent and Nile Valley. Assuming of course they aren't killed by the Wild Magics where the ruin are.

You did forget one thing, the ecological and environmental costs. With Atlas coming "in to phase" with the rest of the world it will screw up the ocean currents, weather patterns, and at least two species of fish will become extinct since a land mass now occupies their breeding grounds. Needless to say Discord would get his wish, a world thrown into chaos.