PFS is already included in Phex (swarming + PFS) with the addition of intelligent segment selection, which downloads rarest segments first.
For i2Phex we'd have to know, how many changes have been made, and if we can integrate the source-code seamlessly.
It could be quite much work, and the i2p-people don't want i2p be widely spread as of now, afaik. So we'd have to make i2phex invisible in the gui, till they decide, that the time of i2ps dawn has come.
Besides: the main devs are GregorK (doing a hell of great work here), I'm only doing a part-time job where I can
.
Sometimes other devs add their contributions
Do you have experience with i2phex?