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?
Although not officially supported – A couple sources (EveryMac, OWC) indicate the late 2012/ early 2013 rMBPs support after market SSD upgrades.
[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.
Best Answer
Update (5/24/2016)
Salvation is here! OWC has released SSD upgrades for the MacBook Pro with Retina Display 13" & 15" Late 2013, 2014, and 2015