Do the late 2013 models (13" - (ME864LL/A, ME865LL/A, ME866LL/A), 15" - (ME293LL/A, ME294LL/A)) support after market SSD upgrades? If so, is a drive that works with the late 2012/ early 2013 rMBPs compatible with the late 2013 models?
[Update] ifixit posted a teardown here indicating in step 8 that:
The proprietary SSD has changed to a PCIe format, but still isn't a standard 2.5" drive. However, it is a separate daughtercard, and we’re hopeful we can offer an upgrade in the near future.