There has been no official announcement of PoE for the Ethernet FeatherWing.
However, as you have figured out, there are three headers on the Ethernet FeatherWing. They’re actually 0.1" two or three pin female sockets and they’re populated on the board from the factory on all units.
One could imagine that at some point in time in the future, there could be a small board with an off-the-shelf 802.3af module on it that sits on top of the Ethernet FeatherWing and plugs into those female header pins…