Honestly did you really think that they would start from scratch. No they couldn't not in 2 years even with cod's resources it just is not practical. Developers have been homing their engine for years since the days of Quake. To create a new engine in 2 or even 4 years would with out a genuine reason to do so would be suicide.
BUT THERE IS A DAM GOOD REASON. fix the problem with non registering bullets because the frame rates don't match up honestly IF you can make all projectiles register then you will have many happy gamers.