Gonna go with not recording yet. Just making an assumption here(and we all know the saying), but given there's a reasonable amount of editting that goes into the voice clips after they're done(like leveling, raising/lowering pitches, etc.), it makes sense to get all of the major actors out of the way first so that editting can be done while the rest of the minor roles can go in.
Thus the reason the only two real confirmations/hints we have are McCartney and Stoner so far. But yeah, I'm just speculating here.
I'm going to go with this, it makes the most sense that they haven't been asked yet. It wouldn't make sense for them to not have voices like Zexion's in 1.5