Up until now, the bottom bar was all for the user: profile, my likes and notifications, search, go home. Profile, home, and search are still there, but right in the middle are two content buttons, dispersing notifications to what looks like the top bar? Is instagram really that focused on pushing content (especially shopping) just a little closer to your thumb? It's all very interesting.

Edit: I missed the main point, the create a post button is gone, making it easier to consume and shop than to add content, and revealing the value of the average user's posts, I guess.