I would argue that Halo is already a bigger franchise than Call of Duty; I'm not sure how Halo as a series can get any bigger than it already is. Other than going multiplat, I guess.
Titanfall had a chance at being the next Call of Duty, but the choice of limiting it to Xbox platforms, and then delaying it on the 360 (where it would have been more successful) are two very dumb choices.
I agree with the Battlefield and Destiny analysis though. Most people like the small maps and more arcade-y feel of Call of Duty games. Battlefield has always been the opposite. I think we are seeing now with the Battlefield 3 and 4 maps that EA is slowly turning Battlefield into Call of Duty -- opting to scale down on the destruction and having some smaller maps with no vehicles in them. Effectively taking away the essence of Battlefield.
Destiny will be the next Call of Duty. Absolutely.