1Tb PCIe SSD in 2012 Retina MacBook Pro? Now that the late 2013 Retina MacBook Pro can be configured with Samsung based 1TB PCIe based SSD storage, would those fit into the late 2012 Retina MacBook Pro?

OWC describes about the 1TB configuration, but not about the specs.
No, the 2012 and early-2013 Retina MBP SSD's are not PCIe-based, so you could not install an SSD from a late-2013 Retina MBP.