The iPhone 6 will not be getting any glass inserts as it is clearly evident in CAD drawings and pictures. But what is interesting is how the top and bottom rounded ends caps are separate parts. In some CAD drawing, they are even rendered a different color. The bodies could well have been made out of the same uni-body aluminum Apple is famous for, but instead are separately attached parts.There would have to be a good reason for that. I am going to go out on a limb and predict that the top and bottom ends will be made out of Liquidmetal.
Those two end pieces are the the parts that would receive the most wear and tear, and unlike aluminum, Liquidmetal is stronger and retains a scratch-free surface longer. If Apple were to begin using Liquidmetal, incrementally on smaller parts would make the most sense.