Considering GT Advanced will be producing $500M-700M worth of sapphire in 2H2014 alone, Apple seems very optimistic that this "secret project" will take off fast.
An iPhone-sized sapphire screen cover is estimated to cost between $9 and $12. That would mean 50 millions of those products would be made in those 6 months alone. Since Apple obviously starts producing their hardware before they go for sale, those 50M units would probably take only ~3 months to sell even though they take 6 months to make.
For reference, it took the original iPhone 74 days to sell 1M units, and it took the iPad 28 days.
Whatever that project is, Apple expects it to sell a lot. As much as I would love it to be a product from an entirely new category, I have a hard time believing it looking at those numbers.