When I got this laptop, it was on the basis I knew there was no way of upgrading the SSD in it, however..
I thought that they used an M.2 interface? If so, shouldn't the release of M.2 on Intel motherboards create an influx of M.2 SSDs and if that happens, do you think they'd fit the MBPr? Would be interesting to find out, and would make the laptop upgradeable (a little).
I've got a 128GB SSD in mine, and with my music database having increased by almost two times in the past month, it's starting to look a little small.