I think Nemesis pins and such should have a lot more reward than a knife kill; this isn't CoD, this is BF we're talking about. I would rather have somebody rewarded for beating me by actual skill, than by some lucky kill with a weapon that's broken, as well.
I don't know, it honestly really pisses me off when I get knifed, especially because the knife never works half of the time, and because it's usually after I shotgun somebody from 2 feet away in the face, which is 100%-certified, Grade-A bullshit. Something tells me the knife may be just as awful in BF3, and have really spotty detection as to whats "front" and "back"