Great find. The key is weight, and how much more expensive sapphire is as compared to Gorilla Glass. Would be really nice to see some phone manufactures express interest, there must be some drawback that is keeping them from moving away from Gorilla Glass.
sapphire is 4 times as dense as water.
gorilla glass is ~2.5 times as denser as water.
I don't know how much the screen cover weighs compared to the entire phone though, the 60% increase might matter very little if it's currently say 5% or 10% of the overall weight. It's quite thin after all.
it can be made 2/3 as thick as gorilla glass for the same weight and still be scratch resistant.
The issue is price though.
"Gorilla Glass at 15 cents per square inch is very attractive relative to sapphire at $3.00 per square inch (at bargain-basement prices)."
This quote is from mid 2012 though. The cost would go down by economy of scale, but not nearly enough I guess.