This could all be fixed if after it was released as the Daily Mission, any day after that running the mission on Heroic Mode would allow you to unlock the content as well. Still you have to wait for Bungie to allow you to get it, which is perplexing but i guess it makes sense. It artificially extends the life of the game. It's a juggling act, put everything in the game and then you have way more gear and weapons to patch and adjust. Introduce it slowly and at your own pace, and then you can see how the weapons and gear impact the game. I would assume this is why they might be doing it, but until Bungie announces why, then it's speculation.