This ROM(XXJP1) has been released. Do *not* flash this ROM.
It works decent, but it does have some major spit and polish issues. Root cannot be obtained via the update.zip method. I tried to revert of UVJE8 via Odin3, and a total hard-brick occurred. Black screen, no button lights, zero. This is not the Cell+!+PC soft-brick. Given the current state of this ROM(engineering preview), it is far from usable as a daily driver. Another user has stated that the cell radio does not work at all.
I say again, if you try to downgrade after flashing XXJP1, you run a very good chance of getting a HARD brick. Avoid.