What I am not in favor for is change for the sake of change. 4e Dark Sun took two of its unique-looking races, Dray and Half-Giants, and made them Dragonborn and Goliath under different names. That weakened what Dark Sun was, and I don't want the same to happen to Greyhawk.
The changes GoS made by adding a Tiefling were positive; none of the old material was contradicted, the setting's tone remained consistent, and a race was introduced that made sense within the context presented. The same can be done with other races like Dragonborn.
EDIT: I think I've made my case here, not sure I have anything more to add.