Well, there's also a huge issue as well. It's an alternate universe, not more land. There's a parallel character to every existing character, and ponies change into humans and vice-versa. However, I imagine that this would start a series of highly-invasive studies as well as tons of new legislation. However, when it comes to trade, physical objects don't seem to have consistent properties traveling through the portal, such as the sudden fact that twilight gains/loses clothing traveling through the portal, how dragons become dogs instead, but magical artifacts like the crown remain completely unchanged. Magic also doesn't naturally exist within the human world, either, so there's have to be strict legislation on that as well, because polluting a world with forces beyond it's comprehension is not a good idea, as we've seen. Cultural exchange would be phenomenal, however, when it comes to the omnivorous diet of humans and treatment of horses, ponies, and like hooved animals, there'd be heavy controversy. (Horses in human world are canon, look at "friendship through the ages") There'd be a huge amount of information shared about both worlds between the worlds, and a lot of progress in quantum physics research with the confirmed possibility of parallel universes. There'd also be a problem involving Celestia's less-than-royalty position in the human world in comparison to the pony one, as well as a huge schism in religion. (You have a princess that RAISES THE SUN?!?) (Celestia's just a PRINCIPAL?!?) there'd be issues with having a border between such distinct countries being the size of a mirror. However, negotiations of embassies within reach of the portals would likely begin immediately, as well as cultural exchange, although a human meeting their counterpart could drive them insane.



Essentially, nobody'd know what to do, and there'd be problems right off the bat with discrimination and sense of identity. If a portal to equestria opened to our world under the same conditions, not even the whole Brony community could handle the situation, no matter how prepared they may think they are.