You will never see the Dutch or Australian's in this game. Australia as a nation is too young, and neither have ever been expansionist nations in their past. If you look at the concept of the game, as well as what game this one is based off of (Sid Meier's Civilization), it will never have smaller, less impactful nations like the ones you're asking for.
Spain could very easily be written into the game. At one point they were THE dominating force in the world.
Mongols could also very easily be written into them game, however they are very closely tied to China, so I doubt that you will see it happen.
America MAYBE, but then they are only a world power in recent years, and didn't even exist as you think of them today when this game starts. British is pretty much the same thing for all intensive purposes.
Germany is already in the game (someone suggested them).
Arabs could also very easily be written into the game, and would actually be a great addition from a historic sense.
Persians are a more likely addition than Arabs, as they are very closely related, and the Persians at one point in history dominated the world.
Egyptians would be cool to see.