So i contacted Blizzard support few minutes ago and they told me that you won't be able to buy Curse of Osiris in their shop even when it officialy releases. You can only buy a season pass. So console players can buy only Curse of Osiris while PC players can only buy a season pass?
As far as I know, the standalone DLC is supposed to become available when CoO is released, but perhaps Blizzard is doing something different. On the other hand, perhaps the rep was confused because the DLC is not currently available. It’s probably best to just wait until 10 am Pacific to see if the standalone DLC is actually available via Blizzard.