Hello Aadwen.
The current developer stance on race specific abilities is that they dont like them and dont expect to have them in Vanguard. It is felt that they tend to make people believe a race is specially suited to a specific purpose and they dont want to pigeonhole any race like that.
As to your race question I would say thats probably a matter of the respective races traditional societial values. High Elves are typically aloof and obsessed with keeping their blood line pure. To bed a human and water that blood line down would likely be taught as a great sin to high elven children at a very young age. Dark Elves on the other hand are typically reclusive and arrogant. They would likely look upon a Human mate as a sign of weakness and would rather die than appear weak. Wood elves however have always been portrayed as having a much less rigid and organized society more interested in peace and tranquility than anything else. It seems to me that this is the only reason you see half-elves on Kojan and not on the other two continents.