Not so fast.
I guess I wasn’t the only one thinking this, but someone decided to ask about the possibility of trading with people from other realms when they enter a crossover battleground together. Well Blizzard was quick to give an answer regarding this:
You will not be able to trade with other people from other realms. You will still only be able to trade with people within your own realm.
Sorry intrepid entreprenuers, looks like Blizzard thought of everything here!