What is this point of this Phil Wood "Rohloff Disc Rotor Compatible Hub"?
They have a 135mm version as well. That should be meant to replace the (rear) Rohloff hub when converting a Rohloff drive train to fixed gear/single speed, while keeping the brake disk. Some people may want to do that at least temporarily, and Rohloff compatible frames (without chain tensioner) are by design a good base for fixed gear/single speed conversion by justs swapping out the back wheel. I can see the appeal of this for people who like single speed MTBs.

Apart from the spare parts advantage you mention I can't really see the point in the similar front wheel hub either (yet the Keirin 110mm one). It probably exists because Phil Wood sometimes lists products which are basically combinations of different options they could make if somebody asked for it.