They want a new game every two years? Sounds like we've uncovered Activision's sequel to Call of Duty. As much as I dislike the company, they know what they're doing. People critize them for milking their franchises, but Activision is fully aware that milking will hurt the IPs in the long run: They love to play a game of risks and trust that they are going to have "the next big thing" in their pipeline once their currently top-selling IP stops selling.
It's a shame for everyone who's involved with the development of the games, though. And I don't think that anyone will particularly sad if one of their gamblings fails.
In case of Bungie, I can't quite understand why Bungie signed the contract. I thought they became independent, so that they can get away from developing the same games over and over again, but now they are forced to constantly develop games of their new IP for at least 8 years. I understand that being an independent developer is hard, but the company who made Halo shouldn't have problems to find publisher who would like to fund their games, right?
On the other hand, game development is so expensive nowadays -- especially when you want to make an AAA game -- that it probably isn't financially viable for a publisher to invest into a game that's not going to spawn a larger franchise.