GPS & Wifi + build like 5D Mark III... Is that even possible? Doesn't 7D also have a pop up flash? Would be weird to drop it from Mark II.
Yes, the 7D does have a pop up flash. Proved useful this past weekend.
If it has GPS and WiFi won't part of it have to be plastic - so surely build quality would be more like 6D ?
If it does and the plastic proportion is more subtle then the intent with the 6D becomes more clear 
Personally if it was an APS 5D mk3, all alloy with no Horrible cheap weak plastic pop up flash I'd be very tempted !
The body is made of magnesium.
Air has a permeability of 1.000 000 37
Magnesium has a permiability of 1.000 12
Steel and iron are around 100
Mu-Metal, used for electromagnet shielding, is around 20,000 to 50,000
Think of permeability as the materials ability to react to (attenuate) radio signals.
In other words, the magnesium body is for all practical purposes, transparent to electromagnetic waves (radio)..... and even if it wasn't, there are dozens of holes through the metal shell.