Its not going to. Have faith in the devs. To add to this we should be glad that we have something to look forward to.
Corrections...
I havent seen or heard of any reliable news of Modern Warfare 3.
Battlefield 3 is done by DICE a europeon company not infinity ward.
MW3 has a site now, actually. Saw it yesterday. Google it if you care.
On topic, I'm sure it'll be great fun no matter how it turns out. One good thing about Beth is they don't make promises like, say, Molyneaux and his team do. Any feature that isn't going to make it all the way there isn't going to be advertised beforehand (excepting Oblivion, but that stuff
was made, they just had to cut back to make it work on the new Xbox), so everything we've seen in stuff so far will be in, I'm sure. Thu'um, dual wielding, the 'classless' system and the whole perk thing are all going to happen as they said they will, or better. Have faith, folks!
EDIT: As Gra Varg said, the biggest worry should probably stability and glitches.