@Rangers
-Race
they have ghastly race that looks like Xur and have triangular space ship in the concept art. They can use those
-Planet
They already have Mercury in the game, complete with the "surface-level loading zone" and a bunch of location thats locked. House of Wolves simply unlock The Lighthouse (it was already there since the E3 video). Or Bungie edit it a bit (like the terminus that got broken up into parts in HoW).
They also have Saturnus or something according to IGN article BEFORE the game released.
Frankly, i think Bungie already have contents for Destiny 2 but their own vision is toooooo big for their own good. So instead of releasing all for Destiny 1 (and Destiny is already exceeding the schedule), they decided to cut them up into Destiny 1, 1,5, then 2.
Destiny 1-1,5 use a bunch of stuff that already available but locked = more development time for Destiny 1,6 - 2.
Destiny 1,6-1,9 mix new content with stuff that already available = more development time for destiny 2.
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here a few more "unused stuff".
- In venus, you can found 2 or 3 "Vex Mailbox". This is explained in Grimoire as something something but not interactable in-game.
- in various planets, you can see unused areas far away from accessible ground. and as we know, Destiny dont need the area to be accessible physically to add them as activity (the game works fine teleporting player to physically far away locations).