Would love to hear some feedback from Asus, but being that the phone has been out for months and it hasn't happened plus I don't think they ever even had it on the Zenfone 5, I have great doubts. I have no idea how you release a phone these days without voLTE but live and learn I guess .
I assume (perhaps incorrectly) it hasn't happened because of at least one of the following reasons:
It would cost money for them to do this the official "right" way.
They don't want to "risk" it not working correctly (potential incompatibility issues) and have to deal with complaints and/or any other fallout.