Are Tunnel FETs (TFETs) already employed in some real world application?
It looks like the answer is 'not yet' for a commercial part. When they come out, they might get a different name, because TFET is already in use as the acronym for Trench FET.

Since I don't have any inside information, I would watch for the parts from manufacturers that already make exotic parts that have intrinsic silicon. For example, Avago Technologies makes PIN diodes. The I in PIN stands for intrinsic.

Intrinsic silicon is not rare. It is just an undoped wafer.