This is a rather dogmatic statement, and one that I certainly do not agree with. But I have noticed that some people on this forum apparently have great difficulty making sense of even the simple things.
Out of curiosity: have you watched the worgen zone play-through videos yet?
This is somewhat irrelevant as Bloodmyst is still intended for the draenei. While players of any race can move to other 10-20 zones of their faction to level, the zones still assume that certain races will be leveling in certain zones (e.g., Forsaken in Silverpine, Draenei in Bloodmyst, Blood Elves in Ghostlands, Humans in Westfall/Redridge, etc.). Nothing is stopping Draenei from leveling in Darkshore, but that is not the default assumption of the game. It is however the default assumption that night elves and worgen will level in Darkshore.That's because Bloodmyst was new at the time, and most people had likely done the Dark Shore quests to death.