The Destiny sequel isn't due out for a while yet, having been reported as releasing sometime in 2017. However today Activision confirmed that there will be a sizeable expansion to the original Destiny later this year.
In a press release Activision said: "Activision Publishing, along with its partners at Bungie, expects to bring a large new expansion to Destiny in 2016 and to release a full game sequel in 2017."
At this stage we've no idea what exactly the expansion is going to bring to the game, and the plans for the game's future shift a lot. Originally we were going to get the sequel sooner, but it was delayed and seemingly now for this expansion.
Bungie expanded upon the news with a blog post that said there'd be a Spring update that would raise the level cap:
Prior to the holiday break we mentioned a second, larger update slated for Spring. That content release will feature a significant Light increase, a bunch of new gear to earn and equip, and new challenges for PvE players seeking some more fun experiences and replayability.
Beyond that, the team is focused on delivering a large expansion later this year, and a full Destiny sequel in 2017.