This game is not subscribe based. So the only way to successfully develop the Destiny world is like 50$ DLC each 3/6 month. You think developers will work for free? After this releasing hype, sales will go down — everyone who wanted to own game already bought it. Free DLC will basically mean, that this game is over, and further development of franchise would be Destiny 2 — new standalone game. No WOW-like expansion. Which is quite unlikely for me.