Sooo...
Destiny I - Fall 2013
Comet I - Fall 2014
Destiny II - Fall 2015
Comet II - Fall 2016
Destiny III - Fall 2017
Comet III - Fall 2018
Destiny IV - Fall 2019
Comet IV - Fall 2020
With smatterings of DLC (presumably) everywhere. Seems a little... I don't know, crazy? Hitching your wagon to Activision until 2020, at that kind of workload, it doesn't exactly inspire confidence in terms of the quality Bungie will be able to impart on these games, and of their ability to hang onto their company culture and sanity if and when things get tight. I hope everything goes flawlessly for them.
Don't tell they are working on Call of Duty: Space Warfare.