updated 02:30 pm EDT, Fri August 29, 2014
May confirm two important points
[Updated with video showing powered-on device] A new set of photos from Feld & Volk and well-known leak source Sonny Dickson show what appears to be a complete logic board for the iPhone 6. Significantly, the board contains both an NXP-made NFC chip and what's believed to be 16GB of Toshiba flash memory. Plans for NFC are now widely reported, and the photos may back a claim that Apple will retain 16GB as an option.
The A8 processor on the board is thought to be a 2GHz, 20nm chip, which would make it far faster than the 1.3GHz 28nm A7 found in the iPhone 5s, iPad Air, and Retina iPad mini. Apple is set to officially announce the iPhone 6 at a press event on September 9.
Update: Feld & Volk has also published a video (below) showing a fully-assembled phone being powered on. It can't get past a "Connect to iTunes" screen, however, since an error message on a connected Mac says that iTunes is unable to reach the iPhone update server due to a missing Internet connection.