I've seen that on the TSI a couple of times with nothing plugged to it. VW and Audi do this.
Our FSI engine has one unused port on the intake manifold. Another mystery of holes on the coil harness...which turns out that Canadian FSI GTI's have screws holding the coil harness onto the rocker cover. So our harness is the same but our rocker cover has no holes to accept the screws.
I'm sure it is there for one purpose, or system, required for a region or country elsewhere in the world but is not required for the rest of the world...so it is deleted.