The granularity of CDDA’s simulation is probably a bit too coarse for FOV to make much sense.
In a manner of speaking we already have it when we’re driving around with limited FOV or headlight cones, but a car can’t trivially turn it’s head a few degrees to get a full 360 view while walking along the way our character could. The other trick there is that a vehicle has many more angles of facing than a character has (32, I think, vs 8).
I suppose if someone wanted to write a mod where head/eye encumbrance applied a more and more restrictive FOV that would be amusing, so if you put on a great helm and a pair of welding goggles you’re basically reduced to a 30 degree slot straight ahead. 
But it wouldn’t be playable. There are no controls for actually handling facing unless you are driving. You’d also need some kind of visible facing markers for all the mobs so that you could make meaningful decisions based on those facings. It’s kind of a big can of worms for a pretty iffy return.