Activision has yet to officially acknowledge the existence of a full-fledged Destiny sequel, but given the publisher's ambitious plans for the franchise, you have to figure sequels are in store.
While at one point Activision and Bungie may have had a schedule of annualized releases (suggested by a contract leaked in 2012), swapping between "full" games and massive expansions, a new report stemming from Kotaku suggest the future of Destiny is "constantly in flux."
Sourcing "people familiar with the goings-on at the studio," the report claims Destiny 2 (which may prove not to have an interative, numbered name) has been shifted from its possible September release. The game's rocky development history, which reportedly included an entire story rewrite, and disappointing launch (it wasn't until The Taken King's release last September that many began to praise Destiny), has presumably threw off the entire schedule. And now, we don't really know what's going on.
Since the release of The Taken King in September, Destiny has been relatively quiet in terms of new content. Sure, we've had some minor events, like December's Sparrow Racing League and the addition of weekly Raid challenges, but it's been nothing substantial like new strikes, raids, or planets. That would suggest Bungie is preparing a larger expansion. When that'll launch, however, appears to be anybody's guess.
On the bright side, Bungie did reveal yesterday a special Valentine's Day-themed event. Starting February 9th, Guardians can participate in Crimson Days, which comes with a new 2v2 Crucible mode called "Crimson Doubles." The event is described sa being "on a scale close to Festival of the Lost," Destiny's Halloween event.