I understand that the mainstream market for the Samsung PCIe SSDs are not available, and the only way to upgrade the SSD is to get one off ebay. How likely will there be PCIe SSD that can be replaced by the user in the near future? I need to know this as I am thinking of buying a new 13" rMBP with 16GB RAM and with either 128GB SSD or 256GM SSD. It all depends whether I can comfortably upgrade the SSD in the future at a reasonable cost? Any word on this? Thanks.