What I (& TC + Sparky, etc.) have all done is to 'prestige' - this is where you reset all unlocks (weapons/perks/equipment) in multiplayer, to progress further & unlock different badges. There is no real advantage (no new guns/perks are unlocked) but you get some new badges & the pleasure of starting from the beginning & using more basic weaponry & learning to love going back to the start, but this time with skills! All in all this has all lead to a little added value to the game & has kept people playing.
However, I think many people want to see either some new weapons or spec-ops/single-player missions - that would lead to some actual replayability.
Rant over...we continue