vpack/vunpack from PackedSIMD VSX is needed in SVP64. it can be implemented using REMAP in an advanced form and as a special SVP64 MV-RM Mode providing an extra (2nd) SUBVL.
from the original discussion (going back a long way) this part of the spec has morphed into some "RM EXTRA" fields for Pack and Unpack. there is also a REMAP mode based on Matrix.