They have, and they haven't.

POE is a task in two parts. One is that the jack has to support the extra pair. The other is that POE is typically 44-57V DC, which is more than enough to free the magic smoke from the pi, so this needs to be delt with.

So the support is in the jack, to bring the power out from the extra pair. But there's no 48-5V convertor, because it's big and expensive. So we get a header for two pairs, 48V out and 5V in, and you buy the 48V dc-dc if you require it.

This lets us have our cake and eat it. We get support in the jack for nice & tidy POE, but we don't get the extra bom cost unless we want it.

Also neat is that I see no reason that battery, UPS, etc boards can't use this same header. Just inject power into the 5v pair and ignore the 48v pair. I'm curious if these pins are before or after the polyfuse - if it's before the polyfuse, it finally solves the argument of whether it's safe to power the board via gpio.