It looks as though Infinity Ward has made a reddit post to debunk internet rumors about loot boxes, and they don't seem to happy about it:
Sigh. There continues to be misinformed and incorrect info being pushed about Modern Warfare. What I can say right now is that we are definitely NOT working on any kind of supply drop or loot box system. Also, functional stuff is unlocked through GAMEPLAY. Stay tuned, we're planning to release info this week.