Did you notice it? Did you open your Instagram app and declared: “hey, that’s different”?
For an app that was predominantly laser focused on mobile photography, it seems Instagram is aggressively trying to innovate and grow by breaking new ground (by, ironically, mimicking other products). To me, that subtle icon change in the navbar wasn’t so subtle. To me it was jarring.
Yes, the camera icon was swapped out for a plus sign. Ali rightfully suggests this has been done to be more universal understood by its now immense audience. Another more potent reason brought forward is that as Instagram is opening up to multiple forms of messaging beyond a single photograph, the camera icon itself becomes obsolete.
The plus is a more general way of saying “add content”. Which means that Instagram is not yet done with copying Snapchat. It may look towards other forms of competition. In the end, it might even start to incorporate Facebook functionality as imaging becomes even more important.