mSATA's reused mini-PCIe card form factor was physically too small to contain all the chips needed for a high capacity SSD, given the capacities per chip that were available when the MacBook Air/Retina were released.
There is a new "NGFF" standard that basically apes Apple's longer form factor with a standardized connector, but I haven't seen any devices that use it yet:
mSATA's reused mini-PCIe card form factor was physically too small to contain all the chips needed for a high capacity SSD, given the capacities per chip that were available when the MacBook Air/Retina were released.
There is a new "NGFF" standard that basically apes Apple's longer form factor with a standardized connector, but I haven't seen any devices that use it yet:
http://www.anandtech.com/show/6293/ngff-ssds-putting-an-end-...