Completely unknown at this point. Demand is higher (way higher) that it was for the iPhone 5s. Walk-ins had to wait 3 or 4 weeks in some cases for the 5s, especially in the higher capacities, and for gold. Production is the unknown for the 6/6+. Apple had way more made for launch, but nobody knows about the next wave of manufacturing. A rough guess would be that it's going to be the same as with the 5s, however Apple may have learned from that fiasco and shored up production.