That contract really was a huge insight into the industry in general, as well as into Bungie's road map, but it was already out-of-date when it went public 4 years ago. A new Marathon is not outside the realm of possibility as Bungie still has the rights to that franchise as well as a massive amount of talent and tech. Destiny seems to have swallowed the whole of their resources and then some, given the involvement of High Moon, but we don't know what the future will hold. If VR gaming takes off, it could even be an experimental project into that. A fan can dream.