Didn't they say later this year without any specifics?
I do wonder how good it would be given the last time I had a Windows device with inbuilt LTE and it was a manual exercise to connect rather than it being always connected like an iPad with LTE. I was keen on it too at first but after thinking about this and seeing the $100+ premium, I decided to just hotspot off my iPhone or iPad, and save myself the hassle of paying for another sim card.
Trying to figure out how in the world I'm going to convince the Mrs. that I need a fully-stocked Surface 3 LTE ($880) to replace my lightly used Dell Venue 8 Pro ($300).