Can the RPi be powered through the USB 2.0 port?
It looks to me that there are two fuses ( top right of board ) on those port power lines and my gut feeling is they will be 100mA, so if that's the case, no, not without replacing or bypassing a fuse, and there may be other issues as well such as socket and track current carrying ability.
It may be possible to link the power line on the USB socket to the GPIO power and bypass any fuse that way.
It would be nice to have full details of the USB socket power circuitry but expect it will come in due course.
This is my understanding of the power arrangement ...