This may not come out as a new “sexy”, hot feature in the new iOS, but I think it’s one of the best; the possibility to use several networks at the same time – Multipath TCP.
Before Multipath TCP you could experience a lost internet connection when you were connected to internet through WiFi, and the connection suddenly went down. All traffic on the phone also went down, instead of just using 3G/4G. This is now possible. If the WIFI-connections goes down, the phone will seamlessly use the fastest connection instead, of the lost WiFi-connection. Great improvement!
I guess this will result in more mobile traffic, but the user experience will improve significantly.