This is becoming a thing- disc brakes on the road. There are advantages besides just the stopping power. The ability to get a little bigger on the tires is a nice plus.
The hydraulic line for the flat mount rear caliper goes inside the down tube. There's a steel tube that the line fits into so that you don't have to do a major fishing expedition to get the line installed.
The frame will be fitted with an Enve disc/road fork. The idea is to make a bike that will take 30-32 tires but still have a fairly short wheelbase. This frame is probably going to see a bit of dirt in between the time on pavement.