In terms of engines, Frostbite 1 was made in 2008 and evolved into Frostbite 2 now in 2011
Call of Duty's engine however is older, the biggest change was probably Call of Duty 4 which was in 2007, the engine was pretty much the same since then with small changes. Working hard, or hardly working?
The mentality between MoH and BF2 being released every two years is the same as Call of Duty's indeed, but the thing is, there's been a Battlefield every year since '08 with Bad Company and this system isn't related to a single franchise, but two different ones, in the end, we'll see how it goes...
My only question is: what's BTK's theme? BF2?...
I can't see why not, BF2's timeline (early 21st century) is quite a bit before Battlefield 3 (set in 2014), so there'll still be quite a few differences.