You have to remember the transfer speeds are limited to the speed of the computer's drive (read from HDD, write to iPhone or vise-versa). If you have a SSD then taking advantage of that extra speed might be useful. Also charge speed with a PC is dependent on the USB header, not necessarily the cable. The lightning cable carries 2.1 amps of power from a regular brick to the iPhone's internal charger, so it can definitely carry USB 3.0's 1.5 amps of power.
My guess is USB 3.0 gets ignored by the phone industry, everyone will switch right to USB 3.1 (USB-C). With the MBP getting a single USB-C port (haha terrible right) and other new phones (Nexus series) there is a good chance the iPhone 7 will have it too. USB-C supports speeds up to 10Gbps and would easily be able to supply an iPhone with 2.1 amps of power.