Speaking in an interview with Edge Magazine, Bungie's community and marketing relations manager Eric Osborne has deemed the fabled ten year content plan for Destiny 'laughable'.
What does exist, which is also more believable, is a 'ten-year agreement' between Bungie and Activision. He states "It just became a narrative. I mean, I drive a Honda Civic. I don't know shit about $500 million. A ten year plan? It's a ten year partnership, it has nothing to do with the game proper."
There you have it, the four games and four expansions deal does exist, but not necessarily just for Destiny.