As far as I know, the only reasons stated for not including SAM was that they already added a Japanese themed job in NIN recently, and DRK fits the theme of Heavensward more. The fact that SAM was even a serious contender and that it is such a popular job with fans, I see no reason for it to never be added. I would definitely expect to see it if we get a Doma expansion or at least patches that have more to do with Doma.

I'm a lot more worried about never seeing Blue Mage.