True, but that reasoning doesn't really apply to Samsung I think. Together with Apple they sell the most cellphones on the planet and have numerous other gadgets with screens such as the gear fit (they cell 54 different cellphone models alone ).
That factory would not only produce glass for one cellphone type but for all future product lines. I think Samsung is easily able to produce and sell (combined) 70 million cellphones, gear fits and other hardware in the next 5 years. I'm not saying that they should and would, but I think Samsung is one of the very few manufacturers that could probably justify such an investment for their own products.
They certainly can, but they won't. It's not in their nature to pioneer things. They usually look at what other people do and follow with their own modifications.