There are a number of small but interesting things from the Cambria schematic leak (that Brad doesn't seem to mention?). 

Like the two 3.5 mm audio ports. So it looks like it'll be Quest 1 style again which is cool. Wonder if it's a single dac or dual. Probably not dual, but would be cool. 

Some of the pics have a facial interface, confirming that there will in fact be one, and it seems that logically they might attach magnetically. But there aren't any images of the bottom part, which makes me think it's possible there will be a bottom cut out for the face tracking. 

The face tracking is a curious thing on this. There seem to be 3 holes on the bottom of the headset, which may be the cameras for the face tracking. The dual rods on each side might be for the charging dock. 

The proximity sensor and its IR illuminator are visible. It may or may not contribute to eye/face tracking. The eye tracking cameras don't seem to be visible anywhere, but notably, the pieces outlining the lenses are quite thick, so it's possible they're hiding cams/IR behind them. It might also be possible they're doing the trick where they're sticking the camera on the side of the screen, to look at your eyes through the pancake lenses. 

The ventilation grill lining the edge of the faceplate is quite notable, although the two fans are not clearly visible in any of the shots. 

The speaker ports are facing downwards rather than towards your head. Might be better since Quest 2's ports were closer to your temples than your ears. 

It seems like rather than adjusting the body of the headset to be farther or closer to your face, the front dial might actually be adjusting the lens assemblies themselves.